diff --git a/java/src/com/android/inputmethod/latin/AutoCorrection.java b/java/src/com/android/inputmethod/latin/AutoCorrection.java
index 32b213e..e0452483 100644
--- a/java/src/com/android/inputmethod/latin/AutoCorrection.java
+++ b/java/src/com/android/inputmethod/latin/AutoCorrection.java
@@ -50,7 +50,7 @@
     }
 
     public static boolean isValidWord(final ConcurrentHashMap<String, Dictionary> dictionaries,
-           CharSequence word, boolean ignoreCase) {
+            CharSequence word, boolean ignoreCase) {
         if (TextUtils.isEmpty(word)) {
             return false;
         }
@@ -74,6 +74,24 @@
         return false;
     }
 
+    public static int getMaxFrequency(final ConcurrentHashMap<String, Dictionary> dictionaries,
+            CharSequence word) {
+        if (TextUtils.isEmpty(word)) {
+            return Dictionary.NOT_A_PROBABILITY;
+        }
+        int maxFreq = -1;
+        for (final String key : dictionaries.keySet()) {
+            if (key.equals(Suggest.DICT_KEY_WHITELIST)) continue;
+            final Dictionary dictionary = dictionaries.get(key);
+            if (null == dictionary) continue;
+            final int tempFreq = dictionary.getFrequency(word);
+            if (tempFreq >= maxFreq) {
+                maxFreq = tempFreq;
+            }
+        }
+        return maxFreq;
+    }
+
     public static boolean allowsToBeAutoCorrected(
             final ConcurrentHashMap<String, Dictionary> dictionaries,
             final CharSequence word, final boolean ignoreCase) {
diff --git a/java/src/com/android/inputmethod/latin/BinaryDictionary.java b/java/src/com/android/inputmethod/latin/BinaryDictionary.java
index cb1069c..d0613bd 100644
--- a/java/src/com/android/inputmethod/latin/BinaryDictionary.java
+++ b/java/src/com/android/inputmethod/latin/BinaryDictionary.java
@@ -201,10 +201,14 @@
 
     @Override
     public boolean isValidWord(CharSequence word) {
-        if (word == null) return false;
+        return getFrequency(word) >= 0;
+    }
+
+    @Override
+    public int getFrequency(CharSequence word) {
+        if (word == null) return -1;
         int[] chars = StringUtils.toCodePointArray(word.toString());
-        final int freq = getFrequencyNative(mNativeDict, chars, chars.length);
-        return freq >= 0;
+        return getFrequencyNative(mNativeDict, chars, chars.length);
     }
 
     // TODO: Add a batch process version (isValidBigramMultiple?) to avoid excessive numbers of jni
diff --git a/java/src/com/android/inputmethod/latin/Dictionary.java b/java/src/com/android/inputmethod/latin/Dictionary.java
index 231e9ab..7cd9bc2 100644
--- a/java/src/com/android/inputmethod/latin/Dictionary.java
+++ b/java/src/com/android/inputmethod/latin/Dictionary.java
@@ -31,6 +31,7 @@
     public static final int UNIGRAM = 0;
     public static final int BIGRAM = 1;
 
+    public static final int NOT_A_PROBABILITY = -1;
     /**
      * Interface to be implemented by classes requesting words to be fetched from the dictionary.
      * @see #getWords(WordComposer, CharSequence, WordCallback, ProximityInfo)
@@ -84,6 +85,10 @@
      */
     abstract public boolean isValidWord(CharSequence word);
 
+    public int getFrequency(CharSequence word) {
+        return NOT_A_PROBABILITY;
+    }
+
     /**
      * Compares the contents of the character array with the typed word and returns true if they
      * are the same.
diff --git a/java/src/com/android/inputmethod/latin/DictionaryCollection.java b/java/src/com/android/inputmethod/latin/DictionaryCollection.java
index f3aa27a..1a05fcd 100644
--- a/java/src/com/android/inputmethod/latin/DictionaryCollection.java
+++ b/java/src/com/android/inputmethod/latin/DictionaryCollection.java
@@ -70,6 +70,18 @@
         return false;
     }
 
+    @Override
+    public int getFrequency(CharSequence word) {
+        int maxFreq = -1;
+        for (int i = mDictionaries.size() - 1; i >= 0; --i) {
+            final int tempFreq = mDictionaries.get(i).getFrequency(word);
+            if (tempFreq >= maxFreq) {
+                maxFreq = tempFreq;
+            }
+        }
+        return maxFreq;
+    }
+
     public boolean isEmpty() {
         return mDictionaries.isEmpty();
     }
diff --git a/java/src/com/android/inputmethod/latin/ExpandableDictionary.java b/java/src/com/android/inputmethod/latin/ExpandableDictionary.java
index 358cd4d..34a92fd 100644
--- a/java/src/com/android/inputmethod/latin/ExpandableDictionary.java
+++ b/java/src/com/android/inputmethod/latin/ExpandableDictionary.java
@@ -84,8 +84,7 @@
     protected interface NextWord {
         public Node getWordNode();
         public int getFrequency();
-        /** FcValue is a bit set */
-        public int getFcValue();
+        public ForgettingCurveParams getFcParams();
         public int notifyTypedAgainAndGetFrequency();
     }
 
@@ -108,8 +107,8 @@
         }
 
         @Override
-        public int getFcValue() {
-            return mFrequency;
+        public ForgettingCurveParams getFcParams() {
+            return null;
         }
 
         @Override
@@ -138,8 +137,8 @@
         }
 
         @Override
-        public int getFcValue() {
-            return mFcp.getFc();
+        public ForgettingCurveParams getFcParams() {
+            return mFcp;
         }
 
         @Override
diff --git a/java/src/com/android/inputmethod/latin/LatinIME.java b/java/src/com/android/inputmethod/latin/LatinIME.java
index 5208881..3854943 100644
--- a/java/src/com/android/inputmethod/latin/LatinIME.java
+++ b/java/src/com/android/inputmethod/latin/LatinIME.java
@@ -2093,8 +2093,12 @@
             } else {
                 secondWord = suggestion.toString();
             }
+            // We demote unrecognized word and words with 0-frequency (assuming they would be
+            // profanity etc.) by specifying them as "invalid".
+            final int maxFreq = AutoCorrection.getMaxFrequency(
+                    mSuggest.getUnigramDictionaries(), suggestion);
             mUserHistoryDictionary.addToUserHistory(null == prevWord ? null : prevWord.toString(),
-                    secondWord);
+                    secondWord, maxFreq > 0);
             return prevWord;
         }
         return null;
diff --git a/java/src/com/android/inputmethod/latin/UserHistoryDictionary.java b/java/src/com/android/inputmethod/latin/UserHistoryDictionary.java
index d5163f2..c8ad40b 100644
--- a/java/src/com/android/inputmethod/latin/UserHistoryDictionary.java
+++ b/java/src/com/android/inputmethod/latin/UserHistoryDictionary.java
@@ -148,7 +148,7 @@
      * context, as in beginning of a sentence for example.
      * The second word may not be null (a NullPointerException would be thrown).
      */
-    public int addToUserHistory(final String word1, String word2) {
+    public int addToUserHistory(final String word1, String word2, boolean isValid) {
         super.addWord(word2, null /* the "shortcut" parameter is null */, FREQUENCY_FOR_TYPED);
         // Do not insert a word as a bigram of itself
         if (word2.equals(word1)) {
@@ -158,7 +158,7 @@
         if (null == word1) {
             freq = FREQUENCY_FOR_TYPED;
         } else {
-            freq = super.setBigramAndGetFrequency(word1, word2, new ForgettingCurveParams());
+            freq = super.setBigramAndGetFrequency(word1, word2, new ForgettingCurveParams(isValid));
         }
         synchronized (mPendingWritesLock) {
             mBigramList.addBigram(word1, word2);
@@ -416,10 +416,11 @@
                         } else {
                             final NextWord nw = mUserHistoryDictionary.getBigramWord(word1, word2);
                             if (nw != null) {
-                                final int tempFreq = nw.getFcValue();
-                                // TODO: Check whether the word is valid or not
+                                final ForgettingCurveParams fcp = nw.getFcParams();
+                                final int tempFreq = fcp.getFc();
+                                final boolean isValid = fcp.isValid();
                                 if (UserHistoryForgettingCurveUtils.needsToSave(
-                                        (byte)tempFreq, false, addLevel0Bigram)) {
+                                        (byte)tempFreq, isValid, addLevel0Bigram)) {
                                     freq = tempFreq;
                                 } else {
                                     freq = -1;
diff --git a/java/src/com/android/inputmethod/latin/UserHistoryForgettingCurveUtils.java b/java/src/com/android/inputmethod/latin/UserHistoryForgettingCurveUtils.java
index feb1d00..9cd8c67 100644
--- a/java/src/com/android/inputmethod/latin/UserHistoryForgettingCurveUtils.java
+++ b/java/src/com/android/inputmethod/latin/UserHistoryForgettingCurveUtils.java
@@ -38,26 +38,39 @@
     public static class ForgettingCurveParams {
         private byte mFc;
         long mLastTouchedTime = 0;
+        private final boolean mIsValid;
 
         private void updateLastTouchedTime() {
             mLastTouchedTime = System.currentTimeMillis();
         }
 
-        public ForgettingCurveParams() {
-            // TODO: Check whether this word is valid or not
-            this(System.currentTimeMillis());
+        public ForgettingCurveParams(boolean isValid) {
+            this(System.currentTimeMillis(), isValid);
         }
 
-        private ForgettingCurveParams(long now) {
-            this((int)pushCount((byte)0, false), now, now);
+        private ForgettingCurveParams(long now, boolean isValid) {
+            this((int)pushCount((byte)0, isValid), now, now, isValid);
         }
 
+        /** This constructor is called when the user history bigram dictionary is being restored. */
         public ForgettingCurveParams(int fc, long now, long last) {
+            // All words with level >= 1 had been saved.
+            // Invalid words with level == 0 had been saved.
+            // Valid words words with level == 0 had *not* been saved.
+            this(fc, now, last, fcToLevel((byte)fc) > 0);
+        }
+
+        private ForgettingCurveParams(int fc, long now, long last, boolean isValid) {
+            mIsValid = isValid;
             mFc = (byte)fc;
             mLastTouchedTime = last;
             updateElapsedTime(now);
         }
 
+        public boolean isValid() {
+            return mIsValid;
+        }
+
         public byte getFc() {
             updateElapsedTime(System.currentTimeMillis());
             return mFc;