diff --git a/java/src/com/android/inputmethod/latin/BinaryDictionary.java b/java/src/com/android/inputmethod/latin/BinaryDictionary.java
index e7ab02a..b775406 100644
--- a/java/src/com/android/inputmethod/latin/BinaryDictionary.java
+++ b/java/src/com/android/inputmethod/latin/BinaryDictionary.java
@@ -191,7 +191,8 @@
     private static native void closeNative(long dict);
     private static native int getFormatVersionNative(long dict);
     private static native int getProbabilityNative(long dict, int[] word);
-    private static native int getBigramProbabilityNative(long dict, int[] word0, int[] word1);
+    private static native int getBigramProbabilityNative(long dict, int[] word0,
+            boolean isBeginningOfSentence, int[] word1);
     private static native void getWordPropertyNative(long dict, int[] word,
             int[] outCodePoints, boolean[] outFlags, int[] outProbabilityInfo,
             ArrayList<int[]> outBigramTargets, ArrayList<int[]> outBigramProbabilityInfo,
@@ -200,15 +201,17 @@
     private static native void getSuggestionsNative(long dict, long proximityInfo,
             long traverseSession, int[] xCoordinates, int[] yCoordinates, int[] times,
             int[] pointerIds, int[] inputCodePoints, int inputSize, int[] suggestOptions,
-            int[] prevWordCodePointArray, int[] outputSuggestionCount, int[] outputCodePoints,
-            int[] outputScores, int[] outputIndices, int[] outputTypes,
-            int[] outputAutoCommitFirstWordConfidence, float[] inOutLanguageWeight);
+            int[] prevWordCodePointArray, boolean isBeginningOfSentence,
+            int[] outputSuggestionCount, int[] outputCodePoints, int[] outputScores,
+            int[] outputIndices, int[] outputTypes, int[] outputAutoCommitFirstWordConfidence,
+            float[] inOutLanguageWeight);
     private static native void addUnigramWordNative(long dict, int[] word, int probability,
-            int[] shortcutTarget, int shortcutProbability, boolean isNotAWord,
-            boolean isBlacklisted, int timestamp);
-    private static native void addBigramWordsNative(long dict, int[] word0, int[] word1,
-            int probability, int timestamp);
-    private static native void removeBigramWordsNative(long dict, int[] word0, int[] word1);
+            int[] shortcutTarget, int shortcutProbability, boolean isBeginningOfSentence,
+            boolean isNotAWord, boolean isBlacklisted, int timestamp);
+    private static native void addBigramWordsNative(long dict, int[] word0,
+            boolean isBeginningOfSentence, int[] word1, int probability, int timestamp);
+    private static native void removeBigramWordsNative(long dict, int[] word0,
+            boolean isBeginningOfSentence, int[] word1);
     private static native int addMultipleDictionaryEntriesNative(long dict,
             LanguageModelParam[] languageModelParams, int startIndex);
     private static native String getPropertyNative(long dict, String query);
@@ -301,7 +304,8 @@
                 getTraverseSession(sessionId).getSession(), inputPointers.getXCoordinates(),
                 inputPointers.getYCoordinates(), inputPointers.getTimes(),
                 inputPointers.getPointerIds(), mInputCodePoints, inputSize,
-                mNativeSuggestOptions.getOptions(), prevWordCodePointArray, mOutputSuggestionCount,
+                mNativeSuggestOptions.getOptions(), prevWordCodePointArray,
+                prevWordsInfo.mIsBeginningOfSentence, mOutputSuggestionCount,
                 mOutputCodePoints, mOutputScores, mSpaceIndices, mOutputTypes,
                 mOutputAutoCommitFirstWordConfidence, mInputOutputLanguageWeight);
         if (inOutLanguageWeight != null) {
@@ -364,12 +368,13 @@
     }
 
     public int getNgramProbability(final PrevWordsInfo prevWordsInfo, final String word) {
-        if (TextUtils.isEmpty(prevWordsInfo.mPrevWord) || TextUtils.isEmpty(word)) {
+        if (!prevWordsInfo.isValid() || TextUtils.isEmpty(word)) {
             return NOT_A_PROBABILITY;
         }
         final int[] codePoints0 = StringUtils.toCodePointArray(prevWordsInfo.mPrevWord);
         final int[] codePoints1 = StringUtils.toCodePointArray(word);
-        return getBigramProbabilityNative(mNativeDict, codePoints0, codePoints1);
+        return getBigramProbabilityNative(mNativeDict, codePoints0,
+                prevWordsInfo.mIsBeginningOfSentence, codePoints1);
     }
 
     public WordProperty getWordProperty(final String word) {
@@ -420,16 +425,17 @@
 
     // Add a unigram entry to binary dictionary with unigram attributes in native code.
     public void addUnigramEntry(final String word, final int probability,
-            final String shortcutTarget, final int shortcutProbability, final boolean isNotAWord,
+            final String shortcutTarget, final int shortcutProbability,
+            final boolean isBeginningOfSentence, final boolean isNotAWord,
             final boolean isBlacklisted, final int timestamp) {
-        if (TextUtils.isEmpty(word)) {
+        if (word == null || (word.isEmpty() && !isBeginningOfSentence)) {
             return;
         }
         final int[] codePoints = StringUtils.toCodePointArray(word);
         final int[] shortcutTargetCodePoints = (shortcutTarget != null) ?
                 StringUtils.toCodePointArray(shortcutTarget) : null;
         addUnigramWordNative(mNativeDict, codePoints, probability, shortcutTargetCodePoints,
-                shortcutProbability, isNotAWord, isBlacklisted, timestamp);
+                shortcutProbability, isBeginningOfSentence, isNotAWord, isBlacklisted, timestamp);
         mHasUpdated = true;
     }
 
@@ -437,23 +443,25 @@
     public void addNgramEntry(final PrevWordsInfo prevWordsInfo, final String word,
             final int probability,
             final int timestamp) {
-        if (TextUtils.isEmpty(prevWordsInfo.mPrevWord) || TextUtils.isEmpty(word)) {
+        if (!prevWordsInfo.isValid() || TextUtils.isEmpty(word)) {
             return;
         }
         final int[] codePoints0 = StringUtils.toCodePointArray(prevWordsInfo.mPrevWord);
         final int[] codePoints1 = StringUtils.toCodePointArray(word);
-        addBigramWordsNative(mNativeDict, codePoints0, codePoints1, probability, timestamp);
+        addBigramWordsNative(mNativeDict, codePoints0, prevWordsInfo.mIsBeginningOfSentence,
+                codePoints1, probability, timestamp);
         mHasUpdated = true;
     }
 
     // Remove an n-gram entry from the binary dictionary in native code.
     public void removeNgramEntry(final PrevWordsInfo prevWordsInfo, final String word) {
-        if (TextUtils.isEmpty(prevWordsInfo.mPrevWord) || TextUtils.isEmpty(word)) {
+        if (!prevWordsInfo.isValid() || TextUtils.isEmpty(word)) {
             return;
         }
         final int[] codePoints0 = StringUtils.toCodePointArray(prevWordsInfo.mPrevWord);
         final int[] codePoints1 = StringUtils.toCodePointArray(word);
-        removeBigramWordsNative(mNativeDict, codePoints0, codePoints1);
+        removeBigramWordsNative(mNativeDict, codePoints0, prevWordsInfo.mIsBeginningOfSentence,
+                codePoints1);
         mHasUpdated = true;
     }
 
diff --git a/java/src/com/android/inputmethod/latin/ExpandableBinaryDictionary.java b/java/src/com/android/inputmethod/latin/ExpandableBinaryDictionary.java
index d67253c..334ebb3 100644
--- a/java/src/com/android/inputmethod/latin/ExpandableBinaryDictionary.java
+++ b/java/src/com/android/inputmethod/latin/ExpandableBinaryDictionary.java
@@ -292,7 +292,7 @@
             final String shortcutTarget, final int shortcutFreq, final boolean isNotAWord,
             final boolean isBlacklisted, final int timestamp) {
         mBinaryDictionary.addUnigramEntry(word, frequency, shortcutTarget, shortcutFreq,
-                isNotAWord, isBlacklisted, timestamp);
+                false /* isBeginningOfSentence */, isNotAWord, isBlacklisted, timestamp);
     }
 
     /**
diff --git a/java/src/com/android/inputmethod/latin/PrevWordsInfo.java b/java/src/com/android/inputmethod/latin/PrevWordsInfo.java
index ecc8947..3494d16 100644
--- a/java/src/com/android/inputmethod/latin/PrevWordsInfo.java
+++ b/java/src/com/android/inputmethod/latin/PrevWordsInfo.java
@@ -20,6 +20,8 @@
 
 // TODO: Support multiple previous words for n-gram.
 public class PrevWordsInfo {
+    public static final PrevWordsInfo BEGINNING_OF_SENTENCE = new PrevWordsInfo();
+
     // The previous word. May be null after resetting and before starting a new composing word, or
     // when there is no context like at the start of text for example. It can also be set to null
     // externally when the user enters a separator that does not let bigrams across, like a period
@@ -32,7 +34,7 @@
 
     // Beginning of sentence.
     public PrevWordsInfo() {
-        mPrevWord = null;
+        mPrevWord = "";
         mIsBeginningOfSentence = true;
     }
 
@@ -40,4 +42,8 @@
         mPrevWord = prevWord;
         mIsBeginningOfSentence = false;
     }
+
+    public boolean isValid() {
+        return mPrevWord != null;
+    }
 }
diff --git a/java/src/com/android/inputmethod/latin/makedict/WordProperty.java b/java/src/com/android/inputmethod/latin/makedict/WordProperty.java
index 8533922..ed83251 100644
--- a/java/src/com/android/inputmethod/latin/makedict/WordProperty.java
+++ b/java/src/com/android/inputmethod/latin/makedict/WordProperty.java
@@ -35,6 +35,8 @@
     public final ProbabilityInfo mProbabilityInfo;
     public final ArrayList<WeightedString> mShortcutTargets;
     public final ArrayList<WeightedString> mBigrams;
+    // TODO: Support mIsBeginningOfSentence.
+    public final boolean mIsBeginningOfSentence;
     public final boolean mIsNotAWord;
     public final boolean mIsBlacklistEntry;
     public final boolean mHasShortcuts;
@@ -51,6 +53,7 @@
         mProbabilityInfo = probabilityInfo;
         mShortcutTargets = shortcutTargets;
         mBigrams = bigrams;
+        mIsBeginningOfSentence = false;
         mIsNotAWord = isNotAWord;
         mIsBlacklistEntry = isBlacklistEntry;
         mHasBigrams = bigrams != null && !bigrams.isEmpty();
@@ -77,6 +80,7 @@
         mProbabilityInfo = createProbabilityInfoFromArray(probabilityInfo);
         mShortcutTargets = CollectionUtils.newArrayList();
         mBigrams = CollectionUtils.newArrayList();
+        mIsBeginningOfSentence = false;
         mIsNotAWord = isNotAWord;
         mIsBlacklistEntry = isBlacklisted;
         mHasShortcuts = hasShortcuts;
diff --git a/native/jni/com_android_inputmethod_latin_BinaryDictionary.cpp b/native/jni/com_android_inputmethod_latin_BinaryDictionary.cpp
index 5ad2114..e41fe1d 100644
--- a/native/jni/com_android_inputmethod_latin_BinaryDictionary.cpp
+++ b/native/jni/com_android_inputmethod_latin_BinaryDictionary.cpp
@@ -178,10 +178,10 @@
         jlong proximityInfo, jlong dicTraverseSession, jintArray xCoordinatesArray,
         jintArray yCoordinatesArray, jintArray timesArray, jintArray pointerIdsArray,
         jintArray inputCodePointsArray, jint inputSize, jintArray suggestOptions,
-        jintArray prevWordCodePointsForBigrams, jintArray outSuggestionCount,
-        jintArray outCodePointsArray, jintArray outScoresArray, jintArray outSpaceIndicesArray,
-        jintArray outTypesArray, jintArray outAutoCommitFirstWordConfidenceArray,
-        jfloatArray inOutLanguageWeight) {
+        jintArray prevWordCodePointsForBigrams, jboolean isBeginningOfSentence,
+        jintArray outSuggestionCount, jintArray outCodePointsArray, jintArray outScoresArray,
+        jintArray outSpaceIndicesArray, jintArray outTypesArray,
+        jintArray outAutoCommitFirstWordConfidenceArray, jfloatArray inOutLanguageWeight) {
     Dictionary *dictionary = reinterpret_cast<Dictionary *>(dict);
     // Assign 0 to outSuggestionCount here in case of returning earlier in this method.
     JniDataUtils::putIntToArray(env, outSuggestionCount, 0 /* index */, 0);
@@ -274,7 +274,7 @@
 }
 
 static jint latinime_BinaryDictionary_getBigramProbability(JNIEnv *env, jclass clazz,
-        jlong dict, jintArray word0, jintArray word1) {
+        jlong dict, jintArray word0, jboolean isBeginningOfSentence, jintArray word1) {
     Dictionary *dictionary = reinterpret_cast<Dictionary *>(dict);
     if (!dictionary) return JNI_FALSE;
     const jsize word0Length = env->GetArrayLength(word0);
@@ -283,7 +283,7 @@
     int word1CodePoints[word1Length];
     env->GetIntArrayRegion(word0, 0, word0Length, word0CodePoints);
     env->GetIntArrayRegion(word1, 0, word1Length, word1CodePoints);
-    const PrevWordsInfo prevWordsInfo(word0CodePoints, word0Length, false /* isStartOfSentence */);
+    const PrevWordsInfo prevWordsInfo(word0CodePoints, word0Length, isBeginningOfSentence);
     return dictionary->getBigramProbability(&prevWordsInfo, word1CodePoints, word1Length);
 }
 
@@ -326,7 +326,8 @@
 
 static void latinime_BinaryDictionary_addUnigramWord(JNIEnv *env, jclass clazz, jlong dict,
         jintArray word, jint probability, jintArray shortcutTarget, jint shortcutProbability,
-        jboolean isNotAWord, jboolean isBlacklisted, jint timestamp) {
+        jboolean isBeginningOfSentence, jboolean isNotAWord, jboolean isBlacklisted,
+        jint timestamp) {
     Dictionary *dictionary = reinterpret_cast<Dictionary *>(dict);
     if (!dictionary) {
         return;
@@ -341,13 +342,14 @@
         shortcuts.emplace_back(&shortcutTargetCodePoints, shortcutProbability);
     }
     // Use 1 for count to indicate the word has inputted.
-    const UnigramProperty unigramProperty(false /* isBeginningOfSentence */, isNotAWord,
+    const UnigramProperty unigramProperty(isBeginningOfSentence, isNotAWord,
             isBlacklisted, probability, timestamp, 0 /* level */, 1 /* count */, &shortcuts);
     dictionary->addUnigramEntry(codePoints, codePointCount, &unigramProperty);
 }
 
 static void latinime_BinaryDictionary_addBigramWords(JNIEnv *env, jclass clazz, jlong dict,
-        jintArray word0, jintArray word1, jint probability, jint timestamp) {
+        jintArray word0, jboolean isBeginningOfSentence, jintArray word1, jint probability,
+        jint timestamp) {
     Dictionary *dictionary = reinterpret_cast<Dictionary *>(dict);
     if (!dictionary) {
         return;
@@ -363,13 +365,12 @@
     // Use 1 for count to indicate the bigram has inputted.
     const BigramProperty bigramProperty(&bigramTargetCodePoints, probability,
             timestamp, 0 /* level */, 1 /* count */);
-    const PrevWordsInfo prevWordsInfo(word0CodePoints, word0Length,
-            false /* isBeginningOfSentence */);
+    const PrevWordsInfo prevWordsInfo(word0CodePoints, word0Length, isBeginningOfSentence);
     dictionary->addNgramEntry(&prevWordsInfo, &bigramProperty);
 }
 
 static void latinime_BinaryDictionary_removeBigramWords(JNIEnv *env, jclass clazz, jlong dict,
-        jintArray word0, jintArray word1) {
+        jintArray word0, jboolean isBeginningOfSentence, jintArray word1) {
     Dictionary *dictionary = reinterpret_cast<Dictionary *>(dict);
     if (!dictionary) {
         return;
@@ -380,8 +381,7 @@
     jsize word1Length = env->GetArrayLength(word1);
     int word1CodePoints[word1Length];
     env->GetIntArrayRegion(word1, 0, word1Length, word1CodePoints);
-    const PrevWordsInfo prevWordsInfo(word0CodePoints, word0Length,
-            false /* isBeginningOfSentence */);
+    const PrevWordsInfo prevWordsInfo(word0CodePoints, word0Length, isBeginningOfSentence);
     dictionary->removeNgramEntry(&prevWordsInfo, word1CodePoints, word1Length);
 }
 
@@ -625,7 +625,7 @@
     },
     {
         const_cast<char *>("getSuggestionsNative"),
-        const_cast<char *>("(JJJ[I[I[I[I[II[I[I[I[I[I[I[I[I[F)V"),
+        const_cast<char *>("(JJJ[I[I[I[I[II[I[IZ[I[I[I[I[I[I[F)V"),
         reinterpret_cast<void *>(latinime_BinaryDictionary_getSuggestions)
     },
     {
@@ -635,7 +635,7 @@
     },
     {
         const_cast<char *>("getBigramProbabilityNative"),
-        const_cast<char *>("(J[I[I)I"),
+        const_cast<char *>("(J[IZ[I)I"),
         reinterpret_cast<void *>(latinime_BinaryDictionary_getBigramProbability)
     },
     {
@@ -651,17 +651,17 @@
     },
     {
         const_cast<char *>("addUnigramWordNative"),
-        const_cast<char *>("(J[II[IIZZI)V"),
+        const_cast<char *>("(J[II[IIZZZI)V"),
         reinterpret_cast<void *>(latinime_BinaryDictionary_addUnigramWord)
     },
     {
         const_cast<char *>("addBigramWordsNative"),
-        const_cast<char *>("(J[I[III)V"),
+        const_cast<char *>("(J[IZ[III)V"),
         reinterpret_cast<void *>(latinime_BinaryDictionary_addBigramWords)
     },
     {
         const_cast<char *>("removeBigramWordsNative"),
-        const_cast<char *>("(J[I[I)V"),
+        const_cast<char *>("(J[IZ[I)V"),
         reinterpret_cast<void *>(latinime_BinaryDictionary_removeBigramWords)
     },
     {
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/pt_common/dynamic_pt_gc_event_listeners.cpp b/native/jni/src/suggest/policyimpl/dictionary/structure/pt_common/dynamic_pt_gc_event_listeners.cpp
index 028e9ec..1f00fc6 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/structure/pt_common/dynamic_pt_gc_event_listeners.cpp
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/pt_common/dynamic_pt_gc_event_listeners.cpp
@@ -56,7 +56,7 @@
         }
     } else {
         mValueStack.back() += 1;
-        if (ptNodeParams->isTerminal()) {
+        if (ptNodeParams->isTerminal() && !ptNodeParams->representsNonWordInfo()) {
             mValidUnigramCount += 1;
         }
     }
diff --git a/tests/src/com/android/inputmethod/latin/BinaryDictionaryDecayingTests.java b/tests/src/com/android/inputmethod/latin/BinaryDictionaryDecayingTests.java
index 2c2fed3..d551cc7 100644
--- a/tests/src/com/android/inputmethod/latin/BinaryDictionaryDecayingTests.java
+++ b/tests/src/com/android/inputmethod/latin/BinaryDictionaryDecayingTests.java
@@ -63,12 +63,16 @@
         super.tearDown();
     }
 
+    private static boolean supportsBeginningOfSentence(final int formatVersion) {
+        return formatVersion >= FormatSpec.VERSION4_DEV;
+    }
+
     private void addUnigramWord(final BinaryDictionary binaryDictionary, final String word,
             final int probability) {
         binaryDictionary.addUnigramEntry(word, probability, "" /* shortcutTarget */,
                 BinaryDictionary.NOT_A_PROBABILITY /* shortcutProbability */,
-                false /* isNotAWord */, false /* isBlacklisted */,
-                mCurrentTime /* timestamp */);
+                false /* isBeginningOfSentence */, false /* isNotAWord */,
+                false /* isBlacklisted */, mCurrentTime /* timestamp */);
     }
 
     private void addBigramWords(final BinaryDictionary binaryDictionary, final String word0,
@@ -631,4 +635,57 @@
         binaryDictionary.close();
         dictFile.delete();
     }
+
+    public void testBeginningOfSentence() {
+        for (final int formatVersion : DICT_FORMAT_VERSIONS) {
+            if (supportsBeginningOfSentence(formatVersion)) {
+                testBeginningOfSentence(formatVersion);
+            }
+        }
+    }
+
+    private void testBeginningOfSentence(final int formatVersion) {
+        setCurrentTimeForTestMode(mCurrentTime);
+        File dictFile = null;
+        try {
+            dictFile = createEmptyDictionaryAndGetFile("TestBinaryDictionary", formatVersion);
+        } catch (IOException e) {
+            fail("IOException while writing an initial dictionary : " + e);
+        }
+        final BinaryDictionary binaryDictionary = new BinaryDictionary(dictFile.getAbsolutePath(),
+                0 /* offset */, dictFile.length(), true /* useFullEditDistance */,
+                Locale.getDefault(), TEST_LOCALE, true /* isUpdatable */);
+
+        binaryDictionary.addUnigramEntry("", DUMMY_PROBABILITY, "" /* shortcutTarget */,
+                BinaryDictionary.NOT_A_PROBABILITY /* shortcutProbability */,
+                true /* isBeginningOfSentence */, true /* isNotAWord */, false /* isBlacklisted */,
+                mCurrentTime);
+        final PrevWordsInfo prevWordsInfoStartOfSentence = PrevWordsInfo.BEGINNING_OF_SENTENCE;
+        addUnigramWord(binaryDictionary, "aaa", DUMMY_PROBABILITY);
+        binaryDictionary.addNgramEntry(prevWordsInfoStartOfSentence, "aaa", DUMMY_PROBABILITY,
+                mCurrentTime);
+        assertTrue(binaryDictionary.isValidNgram(prevWordsInfoStartOfSentence, "aaa"));
+        binaryDictionary.addNgramEntry(prevWordsInfoStartOfSentence, "aaa", DUMMY_PROBABILITY,
+                mCurrentTime);
+        addUnigramWord(binaryDictionary, "bbb", DUMMY_PROBABILITY);
+        binaryDictionary.addNgramEntry(prevWordsInfoStartOfSentence, "bbb", DUMMY_PROBABILITY,
+                mCurrentTime);
+        assertTrue(binaryDictionary.isValidNgram(prevWordsInfoStartOfSentence, "aaa"));
+        assertTrue(binaryDictionary.isValidNgram(prevWordsInfoStartOfSentence, "bbb"));
+
+        forcePassingLongTime(binaryDictionary);
+        assertFalse(binaryDictionary.isValidNgram(prevWordsInfoStartOfSentence, "aaa"));
+        assertFalse(binaryDictionary.isValidNgram(prevWordsInfoStartOfSentence, "bbb"));
+
+        addUnigramWord(binaryDictionary, "aaa", DUMMY_PROBABILITY);
+        binaryDictionary.addNgramEntry(prevWordsInfoStartOfSentence, "aaa", DUMMY_PROBABILITY,
+                mCurrentTime);
+        addUnigramWord(binaryDictionary, "bbb", DUMMY_PROBABILITY);
+        binaryDictionary.addNgramEntry(prevWordsInfoStartOfSentence, "bbb", DUMMY_PROBABILITY,
+                mCurrentTime);
+        assertTrue(binaryDictionary.isValidNgram(prevWordsInfoStartOfSentence, "aaa"));
+        assertTrue(binaryDictionary.isValidNgram(prevWordsInfoStartOfSentence, "bbb"));
+        binaryDictionary.close();
+        dictFile.delete();
+    }
 }
diff --git a/tests/src/com/android/inputmethod/latin/BinaryDictionaryTests.java b/tests/src/com/android/inputmethod/latin/BinaryDictionaryTests.java
index 2b82e54..31ad344 100644
--- a/tests/src/com/android/inputmethod/latin/BinaryDictionaryTests.java
+++ b/tests/src/com/android/inputmethod/latin/BinaryDictionaryTests.java
@@ -50,6 +50,10 @@
         return formatVersion >= FormatSpec.VERSION4_DEV;
     }
 
+    private static boolean supportsBeginningOfSentence(final int formatVersion) {
+        return formatVersion >= FormatSpec.VERSION4_DEV;
+    }
+
     private File createEmptyDictionaryAndGetFile(final String dictId,
             final int formatVersion) throws IOException {
         if (formatVersion == FormatSpec.VERSION4
@@ -171,7 +175,8 @@
         addUnigramWord(binaryDictionary, invalidLongWord, probability);
         // Too long short cut.
         binaryDictionary.addUnigramEntry("a", probability, invalidLongWord,
-                10 /* shortcutProbability */, false /* isNotAWord */, false /* isBlacklisted */,
+                10 /* shortcutProbability */, false /* isBeginningOfSentence */,
+                false /* isNotAWord */, false /* isBlacklisted */,
                 BinaryDictionary.NOT_A_VALID_TIMESTAMP);
         addUnigramWord(binaryDictionary, "abc", probability);
         final int updatedProbability = 200;
@@ -192,8 +197,8 @@
             final int probability) {
         binaryDictionary.addUnigramEntry(word, probability, "" /* shortcutTarget */,
                 BinaryDictionary.NOT_A_PROBABILITY /* shortcutProbability */,
-                false /* isNotAWord */, false /* isBlacklisted */,
-                BinaryDictionary.NOT_A_VALID_TIMESTAMP /* timestamp */);
+                false /* isBeginningOfSentence */, false /* isNotAWord */,
+                false /* isBlacklisted */, BinaryDictionary.NOT_A_VALID_TIMESTAMP /* timestamp */);
     }
 
     private static void addBigramWords(final BinaryDictionary binaryDictionary, final String word0,
@@ -1010,7 +1015,8 @@
             // TODO: Add tests for historical info.
             binaryDictionary.addUnigramEntry(word, unigramProbability,
                     null /* shortcutTarget */, BinaryDictionary.NOT_A_PROBABILITY,
-                    isNotAWord, isBlacklisted, BinaryDictionary.NOT_A_VALID_TIMESTAMP);
+                    false /* isBeginningOfSentence */, isNotAWord, isBlacklisted,
+                    BinaryDictionary.NOT_A_VALID_TIMESTAMP);
             if (binaryDictionary.needsToRunGC(false /* mindsBlockByGC */)) {
                 binaryDictionary.flushWithGC();
             }
@@ -1188,24 +1194,24 @@
         final int unigramProbability = 100;
         final int shortcutProbability = 10;
         binaryDictionary.addUnigramEntry("aaa", unigramProbability, "zzz",
-                shortcutProbability, false /* isNotAWord */, false /* isBlacklisted */,
-                0 /* timestamp */);
+                shortcutProbability, false /* isBeginningOfSentence */,
+                false /* isNotAWord */, false /* isBlacklisted */, 0 /* timestamp */);
         WordProperty wordProperty = binaryDictionary.getWordProperty("aaa");
         assertEquals(1, wordProperty.mShortcutTargets.size());
         assertEquals("zzz", wordProperty.mShortcutTargets.get(0).mWord);
         assertEquals(shortcutProbability, wordProperty.mShortcutTargets.get(0).getProbability());
         final int updatedShortcutProbability = 2;
         binaryDictionary.addUnigramEntry("aaa", unigramProbability, "zzz",
-                updatedShortcutProbability, false /* isNotAWord */, false /* isBlacklisted */,
-                0 /* timestamp */);
+                updatedShortcutProbability, false /* isBeginningOfSentence */,
+                false /* isNotAWord */, false /* isBlacklisted */, 0 /* timestamp */);
         wordProperty = binaryDictionary.getWordProperty("aaa");
         assertEquals(1, wordProperty.mShortcutTargets.size());
         assertEquals("zzz", wordProperty.mShortcutTargets.get(0).mWord);
         assertEquals(updatedShortcutProbability,
                 wordProperty.mShortcutTargets.get(0).getProbability());
         binaryDictionary.addUnigramEntry("aaa", unigramProbability, "yyy",
-                shortcutProbability, false /* isNotAWord */, false /* isBlacklisted */,
-                0 /* timestamp */);
+                shortcutProbability, false /* isBeginningOfSentence */, false /* isNotAWord */,
+                false /* isBlacklisted */, 0 /* timestamp */);
         final HashMap<String, Integer> shortcutTargets = new HashMap<String, Integer>();
         shortcutTargets.put("zzz", updatedShortcutProbability);
         shortcutTargets.put("yyy", shortcutProbability);
@@ -1275,8 +1281,8 @@
             final String word = words.get(random.nextInt(words.size()));
             final int unigramProbability = unigramProbabilities.get(word);
             binaryDictionary.addUnigramEntry(word, unigramProbability, shortcutTarget,
-                    shortcutProbability, false /* isNotAWord */, false /* isBlacklisted */,
-                    0 /* timestamp */);
+                    shortcutProbability, false /* isBeginningOfSentence */, false /* isNotAWord */,
+                    false /* isBlacklisted */, 0 /* timestamp */);
             if (shortcutTargets.containsKey(word)) {
                 final HashMap<String, Integer> shortcutTargetsOfWord = shortcutTargets.get(word);
                 shortcutTargetsOfWord.put(shortcutTarget, shortcutProbability);
@@ -1331,10 +1337,11 @@
         addBigramWords(binaryDictionary, "aaa", "bbb", bigramProbability);
         final int shortcutProbability = 10;
         binaryDictionary.addUnigramEntry("ccc", unigramProbability, "xxx", shortcutProbability,
-                false /* isNotAWord */, false /* isBlacklisted */, 0 /* timestamp */);
+                false /* isBeginningOfSentence */, false /* isNotAWord */,
+                false /* isBlacklisted */, 0 /* timestamp */);
         binaryDictionary.addUnigramEntry("ddd", unigramProbability, null /* shortcutTarget */,
-                Dictionary.NOT_A_PROBABILITY, true /* isNotAWord */,
-                true /* isBlacklisted */, 0 /* timestamp */);
+                Dictionary.NOT_A_PROBABILITY, false /* isBeginningOfSentence */,
+                true /* isNotAWord */, true /* isBlacklisted */, 0 /* timestamp */);
         assertEquals(unigramProbability, binaryDictionary.getFrequency("aaa"));
         assertEquals(unigramProbability, binaryDictionary.getFrequency("bbb"));
         assertTrue(isValidBigram(binaryDictionary, "aaa", "bbb"));
@@ -1434,4 +1441,46 @@
         assertEquals(bigramProbabilities.size(), Integer.parseInt(
                 binaryDictionary.getPropertyForTest(BinaryDictionary.BIGRAM_COUNT_QUERY)));
     }
+
+    public void testBeginningOfSentence() {
+        for (final int formatVersion : DICT_FORMAT_VERSIONS) {
+            if (supportsBeginningOfSentence(formatVersion)) {
+                testBeginningOfSentence(formatVersion);
+            }
+        }
+    }
+
+    private void testBeginningOfSentence(final int formatVersion) {
+        File dictFile = null;
+        try {
+            dictFile = createEmptyDictionaryAndGetFile("TestBinaryDictionary", formatVersion);
+        } catch (IOException e) {
+            fail("IOException while writing an initial dictionary : " + e);
+        }
+        final BinaryDictionary binaryDictionary = new BinaryDictionary(dictFile.getAbsolutePath(),
+                0 /* offset */, dictFile.length(), true /* useFullEditDistance */,
+                Locale.getDefault(), TEST_LOCALE, true /* isUpdatable */);
+        final int dummyProbability = 0;
+        binaryDictionary.addUnigramEntry("", dummyProbability, "" /* shortcutTarget */,
+                BinaryDictionary.NOT_A_PROBABILITY /* shortcutProbability */,
+                true /* isBeginningOfSentence */, true /* isNotAWord */, false /* isBlacklisted */,
+                BinaryDictionary.NOT_A_VALID_TIMESTAMP /* timestamp */);
+        final PrevWordsInfo prevWordsInfoStartOfSentence = PrevWordsInfo.BEGINNING_OF_SENTENCE;
+        final int bigramProbability = 200;
+        addUnigramWord(binaryDictionary, "aaa", dummyProbability);
+        binaryDictionary.addNgramEntry(prevWordsInfoStartOfSentence, "aaa", bigramProbability,
+                BinaryDictionary.NOT_A_VALID_TIMESTAMP /* timestamp */);
+        assertEquals(bigramProbability,
+                binaryDictionary.getNgramProbability(prevWordsInfoStartOfSentence, "aaa"));
+        binaryDictionary.addNgramEntry(prevWordsInfoStartOfSentence, "aaa", bigramProbability,
+                BinaryDictionary.NOT_A_VALID_TIMESTAMP /* timestamp */);
+        addUnigramWord(binaryDictionary, "bbb", dummyProbability);
+        binaryDictionary.addNgramEntry(prevWordsInfoStartOfSentence, "bbb", bigramProbability,
+                BinaryDictionary.NOT_A_VALID_TIMESTAMP /* timestamp */);
+        binaryDictionary.flushWithGC();
+        assertEquals(bigramProbability,
+                binaryDictionary.getNgramProbability(prevWordsInfoStartOfSentence, "aaa"));
+        assertEquals(bigramProbability,
+                binaryDictionary.getNgramProbability(prevWordsInfoStartOfSentence, "bbb"));
+    }
 }
diff --git a/tests/src/com/android/inputmethod/latin/makedict/Ver4DictEncoder.java b/tests/src/com/android/inputmethod/latin/makedict/Ver4DictEncoder.java
index a04b810..0528e34 100644
--- a/tests/src/com/android/inputmethod/latin/makedict/Ver4DictEncoder.java
+++ b/tests/src/com/android/inputmethod/latin/makedict/Ver4DictEncoder.java
@@ -77,14 +77,14 @@
             if (null == wordProperty.mShortcutTargets || wordProperty.mShortcutTargets.isEmpty()) {
                 binaryDict.addUnigramEntry(wordProperty.mWord, wordProperty.getProbability(),
                         null /* shortcutTarget */, 0 /* shortcutProbability */,
-                        wordProperty.mIsNotAWord, wordProperty.mIsBlacklistEntry,
-                        0 /* timestamp */);
+                        wordProperty.mIsBeginningOfSentence, wordProperty.mIsNotAWord,
+                        wordProperty.mIsBlacklistEntry, 0 /* timestamp */);
             } else {
                 for (final WeightedString shortcutTarget : wordProperty.mShortcutTargets) {
                     binaryDict.addUnigramEntry(wordProperty.mWord, wordProperty.getProbability(),
                             shortcutTarget.mWord, shortcutTarget.getProbability(),
-                            wordProperty.mIsNotAWord, wordProperty.mIsBlacklistEntry,
-                            0 /* timestamp */);
+                            wordProperty.mIsBeginningOfSentence, wordProperty.mIsNotAWord,
+                            wordProperty.mIsBlacklistEntry, 0 /* timestamp */);
                 }
             }
             if (binaryDict.needsToRunGC(true /* mindsBlockByGC */)) {