diff --git a/java/src/com/android/inputmethod/latin/makedict/BinaryDictDecoderUtils.java b/java/src/com/android/inputmethod/latin/makedict/BinaryDictDecoderUtils.java
index 3691845..9f23459 100644
--- a/java/src/com/android/inputmethod/latin/makedict/BinaryDictDecoderUtils.java
+++ b/java/src/com/android/inputmethod/latin/makedict/BinaryDictDecoderUtils.java
@@ -511,7 +511,7 @@
                         final WeightedString word = getWordAtPosition(dictDecoder, headerSize,
                                 bigram.mAddress, options);
                         final int reconstructedFrequency =
-                                BinaryDictIOUtils.reconstructBigramFrequency(word.mFrequency,
+                                BinaryDictIOUtils.reconstructBigramFrequency(word.getProbability(),
                                         bigram.mFrequency);
                         bigrams.add(new WeightedString(word.mWord, reconstructedFrequency));
                     }
@@ -618,7 +618,7 @@
                 // words that are not also registered as unigrams so we don't have to avoid
                 // them explicitly here.
                 for (final WeightedString bigram : w.mBigrams) {
-                    newDict.setBigram(w.mWord, bigram.mWord, bigram.mFrequency);
+                    newDict.setBigram(w.mWord, bigram.mWord, bigram.getProbability());
                 }
             }
         }
diff --git a/java/src/com/android/inputmethod/latin/makedict/FusionDictionary.java b/java/src/com/android/inputmethod/latin/makedict/FusionDictionary.java
index 5b0e839..ef23acb 100644
--- a/java/src/com/android/inputmethod/latin/makedict/FusionDictionary.java
+++ b/java/src/com/android/inputmethod/latin/makedict/FusionDictionary.java
@@ -67,29 +67,40 @@
     }
 
     /**
-     * A string with a frequency.
+     * A string with a probability.
      *
      * This represents an "attribute", that is either a bigram or a shortcut.
      */
     public static final class WeightedString {
         public final String mWord;
-        public int mFrequency;
-        public WeightedString(String word, int frequency) {
+        public ProbabilityInfo mProbabilityInfo;
+
+        public WeightedString(final String word, final int probability) {
             mWord = word;
-            mFrequency = frequency;
+            mProbabilityInfo = new ProbabilityInfo(probability);
+        }
+
+        public int getProbability() {
+            return mProbabilityInfo.mProbability;
+        }
+
+        public void setProbability(final int probability) {
+            mProbabilityInfo = new ProbabilityInfo(probability);
         }
 
         @Override
         public int hashCode() {
-            return Arrays.hashCode(new Object[] { mWord, mFrequency });
+            return Arrays.hashCode(new Object[] { mWord, mProbabilityInfo.mProbability,
+                    mProbabilityInfo.mTimestamp, mProbabilityInfo.mLevel,
+                    mProbabilityInfo.mCount });
         }
 
         @Override
         public boolean equals(Object o) {
             if (o == this) return true;
             if (!(o instanceof WeightedString)) return false;
-            WeightedString w = (WeightedString)o;
-            return mWord.equals(w.mWord) && mFrequency == w.mFrequency;
+            final WeightedString w = (WeightedString)o;
+            return mWord.equals(w.mWord) && mProbabilityInfo.equals(w.mProbabilityInfo);
         }
     }
 
@@ -200,18 +211,18 @@
         }
 
         /**
-         * Adds a word to the bigram list. Updates the frequency if the word already
+         * Adds a word to the bigram list. Updates the probability if the word already
          * exists.
          */
-        public void addBigram(final String word, final int frequency) {
+        public void addBigram(final String word, final int probability) {
             if (mBigrams == null) {
                 mBigrams = new ArrayList<WeightedString>();
             }
             WeightedString bigram = getBigram(word);
             if (bigram != null) {
-                bigram.mFrequency = frequency;
+                bigram.setProbability(probability);
             } else {
-                bigram = new WeightedString(word, frequency);
+                bigram = new WeightedString(word, probability);
                 mBigrams.add(bigram);
             }
         }
@@ -273,8 +284,8 @@
                         final WeightedString existingShortcut = getShortcut(shortcut.mWord);
                         if (existingShortcut == null) {
                             mShortcutTargets.add(shortcut);
-                        } else if (existingShortcut.mFrequency < shortcut.mFrequency) {
-                            existingShortcut.mFrequency = shortcut.mFrequency;
+                        } else if (existingShortcut.getProbability() < shortcut.getProbability()) {
+                            existingShortcut.setProbability(shortcut.getProbability());
                         }
                     }
                 }
@@ -289,8 +300,8 @@
                         final WeightedString existingBigram = getBigram(bigram.mWord);
                         if (existingBigram == null) {
                             mBigrams.add(bigram);
-                        } else if (existingBigram.mFrequency < bigram.mFrequency) {
-                            existingBigram.mFrequency = bigram.mFrequency;
+                        } else if (existingBigram.getProbability() < bigram.getProbability()) {
+                            existingBigram.setProbability(bigram.getProbability());
                         }
                     }
                 }
diff --git a/java/src/com/android/inputmethod/latin/makedict/ProbabilityInfo.java b/java/src/com/android/inputmethod/latin/makedict/ProbabilityInfo.java
index c1a43ce..79f924c 100644
--- a/java/src/com/android/inputmethod/latin/makedict/ProbabilityInfo.java
+++ b/java/src/com/android/inputmethod/latin/makedict/ProbabilityInfo.java
@@ -17,6 +17,7 @@
 package com.android.inputmethod.latin.makedict;
 
 import com.android.inputmethod.latin.BinaryDictionary;
+import com.android.inputmethod.latin.makedict.FusionDictionary.WeightedString;
 
 public final class ProbabilityInfo {
     public final int mProbability;
@@ -39,8 +40,24 @@
         mCount = count;
     }
 
+    public boolean hasHistoricalInfo() {
+        return mTimestamp != BinaryDictionary.NOT_A_VALID_TIMESTAMP;
+    }
+
     @Override
     public String toString() {
         return mTimestamp + ":" + mLevel + ":" + mCount;
     }
+
+    @Override
+    public boolean equals(Object o) {
+      if (o == this) return true;
+      if (!(o instanceof ProbabilityInfo)) return false;
+      final ProbabilityInfo p = (ProbabilityInfo)o;
+      if (!hasHistoricalInfo() && !p.hasHistoricalInfo()) {
+          return mProbability == p.mProbability;
+      }
+      return mProbability == p.mProbability && mTimestamp == p.mTimestamp && mLevel == p.mLevel
+              && mCount == p.mCount;
+  }
 }
\ No newline at end of file
diff --git a/java/src/com/android/inputmethod/latin/makedict/Ver2DictEncoder.java b/java/src/com/android/inputmethod/latin/makedict/Ver2DictEncoder.java
index a3a6c2c..3de083e 100644
--- a/java/src/com/android/inputmethod/latin/makedict/Ver2DictEncoder.java
+++ b/java/src/com/android/inputmethod/latin/makedict/Ver2DictEncoder.java
@@ -197,7 +197,7 @@
             final WeightedString target = shortcutIterator.next();
             final int shortcutFlags = BinaryDictEncoderUtils.makeShortcutFlags(
                     shortcutIterator.hasNext(),
-                    target.mFrequency);
+                    target.getProbability());
             mPosition = BinaryDictEncoderUtils.writeUIntToBuffer(mBuffer, mPosition, shortcutFlags,
                     FormatSpec.PTNODE_ATTRIBUTE_FLAGS_SIZE);
             final int shortcutShift = CharEncoding.writeString(mBuffer, mPosition, target.mWord);
@@ -231,7 +231,7 @@
             final int offset = addressOfBigram
                     - (mPosition + FormatSpec.PTNODE_ATTRIBUTE_FLAGS_SIZE);
             final int bigramFlags = BinaryDictEncoderUtils.makeBigramFlags(bigramIterator.hasNext(),
-                    offset, bigram.mFrequency, unigramFrequencyForThisWord, bigram.mWord);
+                    offset, bigram.getProbability(), unigramFrequencyForThisWord, bigram.mWord);
             mPosition = BinaryDictEncoderUtils.writeUIntToBuffer(mBuffer, mPosition, bigramFlags,
                     FormatSpec.PTNODE_ATTRIBUTE_FLAGS_SIZE);
             mPosition += BinaryDictEncoderUtils.writeChildrenPosition(mBuffer, mPosition,
diff --git a/java/src/com/android/inputmethod/latin/makedict/Ver4DictEncoder.java b/java/src/com/android/inputmethod/latin/makedict/Ver4DictEncoder.java
index 4b0efba..a5b0135 100644
--- a/java/src/com/android/inputmethod/latin/makedict/Ver4DictEncoder.java
+++ b/java/src/com/android/inputmethod/latin/makedict/Ver4DictEncoder.java
@@ -80,7 +80,7 @@
             } else {
                 for (final WeightedString shortcutTarget : word.mShortcutTargets) {
                     binaryDict.addUnigramWord(word.mWord, word.mFrequency,
-                            shortcutTarget.mWord, shortcutTarget.mFrequency,
+                            shortcutTarget.mWord, shortcutTarget.getProbability(),
                             word.mIsNotAWord, word.mIsBlacklistEntry, 0 /* timestamp */);
                 }
             }
@@ -91,7 +91,7 @@
         for (final Word word0 : dict) {
             if (null == word0.mBigrams) continue;
             for (final WeightedString word1 : word0.mBigrams) {
-                binaryDict.addBigramWords(word0.mWord, word1.mWord, word1.mFrequency,
+                binaryDict.addBigramWords(word0.mWord, word1.mWord, word1.getProbability(),
                         0 /* timestamp */);
                 if (binaryDict.needsToRunGC(true /* mindsBlockByGC */)) {
                     binaryDict.flushWithGC();
diff --git a/java/src/com/android/inputmethod/latin/utils/WordProperty.java b/java/src/com/android/inputmethod/latin/utils/WordProperty.java
index da56b21..37d1102 100644
--- a/java/src/com/android/inputmethod/latin/utils/WordProperty.java
+++ b/java/src/com/android/inputmethod/latin/utils/WordProperty.java
@@ -108,7 +108,7 @@
         for (int i = 0; i < mBigramTargets.size(); i++) {
             builder.append("  bigram=" + mBigramTargets.get(i).mWord);
             builder.append(",");
-            builder.append("f=" + mBigramTargets.get(i).mFrequency);
+            builder.append("f=" + mBigramTargets.get(i).getProbability());
             if (mBigramProbabilityInfo.get(i).mTimestamp
                     != BinaryDictionary.NOT_A_VALID_TIMESTAMP) {
                 builder.append(",");
@@ -119,7 +119,7 @@
         for (int i = 0; i < mShortcutTargets.size(); i++) {
             builder.append("  shortcut=" + mShortcutTargets.get(i).mWord);
             builder.append(",");
-            builder.append("f=" + mShortcutTargets.get(i).mFrequency);
+            builder.append("f=" + mShortcutTargets.get(i).getProbability());
             builder.append("\n");
         }
         return builder.toString();
diff --git a/tests/src/com/android/inputmethod/latin/BinaryDictionaryTests.java b/tests/src/com/android/inputmethod/latin/BinaryDictionaryTests.java
index e21975d..b1bdef8 100644
--- a/tests/src/com/android/inputmethod/latin/BinaryDictionaryTests.java
+++ b/tests/src/com/android/inputmethod/latin/BinaryDictionaryTests.java
@@ -962,7 +962,7 @@
             for (int j = 0; j < unigramProperty.mBigramTargets.size(); j++) {
                 final String word1 = unigramProperty.mBigramTargets.get(j).mWord;
                 assertTrue(bigramWord1s.contains(word1));
-                final int probability = unigramProperty.mBigramTargets.get(j).mFrequency;
+                final int probability = unigramProperty.mBigramTargets.get(j).getProbability();
                 assertEquals((int)bigramProbabilities.get(new Pair<String, String>(word0, word1)),
                         probability);
                 assertEquals(unigramProperty.mBigramProbabilityInfo.get(j).mProbability,
@@ -1053,7 +1053,7 @@
             for (int j = 0; j < wordProperty.mBigramTargets.size(); j++) {
                 final String word1 = wordProperty.mBigramTargets.get(j).mWord;
                 assertTrue(bigramWord1s.contains(word1));
-                final int probability = wordProperty.mBigramTargets.get(j).mFrequency;
+                final int probability = wordProperty.mBigramTargets.get(j).getProbability();
                 final Pair<String, String> bigram = new Pair<String, String>(word0, word1);
                 assertEquals((int)bigramProbabilitiesToCheckLater.get(bigram), probability);
                 bigramSet.remove(bigram);
@@ -1087,7 +1087,7 @@
         WordProperty wordProperty = binaryDictionary.getWordProperty("aaa");
         assertEquals(1, wordProperty.mShortcutTargets.size());
         assertEquals("zzz", wordProperty.mShortcutTargets.get(0).mWord);
-        assertEquals(shortcutProbability, wordProperty.mShortcutTargets.get(0).mFrequency);
+        assertEquals(shortcutProbability, wordProperty.mShortcutTargets.get(0).getProbability());
         final int updatedShortcutProbability = 2;
         binaryDictionary.addUnigramWord("aaa", unigramProbability, "zzz",
                 updatedShortcutProbability, false /* isNotAWord */, false /* isBlacklisted */,
@@ -1096,7 +1096,7 @@
         assertEquals(1, wordProperty.mShortcutTargets.size());
         assertEquals("zzz", wordProperty.mShortcutTargets.get(0).mWord);
         assertEquals(updatedShortcutProbability,
-                wordProperty.mShortcutTargets.get(0).mFrequency);
+                wordProperty.mShortcutTargets.get(0).getProbability());
         binaryDictionary.addUnigramWord("aaa", unigramProbability, "yyy",
                 shortcutProbability, false /* isNotAWord */, false /* isBlacklisted */,
                 0 /* timestamp */);
@@ -1107,7 +1107,8 @@
         assertEquals(2, wordProperty.mShortcutTargets.size());
         for (WeightedString shortcutTarget : wordProperty.mShortcutTargets) {
             assertTrue(shortcutTargets.containsKey(shortcutTarget.mWord));
-            assertEquals((int)shortcutTargets.get(shortcutTarget.mWord), shortcutTarget.mFrequency);
+            assertEquals((int)shortcutTargets.get(shortcutTarget.mWord),
+                    shortcutTarget.getProbability());
             shortcutTargets.remove(shortcutTarget.mWord);
         }
         shortcutTargets.put("zzz", updatedShortcutProbability);
@@ -1117,7 +1118,8 @@
         assertEquals(2, wordProperty.mShortcutTargets.size());
         for (WeightedString shortcutTarget : wordProperty.mShortcutTargets) {
             assertTrue(shortcutTargets.containsKey(shortcutTarget.mWord));
-            assertEquals((int)shortcutTargets.get(shortcutTarget.mWord), shortcutTarget.mFrequency);
+            assertEquals((int)shortcutTargets.get(shortcutTarget.mWord),
+                    shortcutTarget.getProbability());
             shortcutTargets.remove(shortcutTarget.mWord);
         }
     }
@@ -1193,7 +1195,7 @@
             for (final WeightedString shortcutTarget : wordProperty.mShortcutTargets) {
                 final String targetCodePonts = shortcutTarget.mWord;
                 assertEquals((int)shortcutTargets.get(word).get(targetCodePonts),
-                        shortcutTarget.mFrequency);
+                        shortcutTarget.getProbability());
             }
         }
     }
diff --git a/tools/dicttool/src/com/android/inputmethod/latin/dicttool/CombinedInputOutput.java b/tools/dicttool/src/com/android/inputmethod/latin/dicttool/CombinedInputOutput.java
index 16f82da..b984060 100644
--- a/tools/dicttool/src/com/android/inputmethod/latin/dicttool/CombinedInputOutput.java
+++ b/tools/dicttool/src/com/android/inputmethod/latin/dicttool/CombinedInputOutput.java
@@ -127,7 +127,7 @@
                 if (null != word) {
                     dict.add(word, freq, shortcuts.isEmpty() ? null : shortcuts, isNotAWord);
                     for (WeightedString s : bigrams) {
-                        dict.setBigram(word, s.mWord, s.mFrequency);
+                        dict.setBigram(word, s.mWord, s.getProbability());
                     }
                 }
                 if (!shortcuts.isEmpty()) shortcuts = new ArrayList<WeightedString>();
@@ -185,7 +185,7 @@
         if (null != word) {
             dict.add(word, freq, shortcuts.isEmpty() ? null : shortcuts, isNotAWord);
             for (WeightedString s : bigrams) {
-                dict.setBigram(word, s.mWord, s.mFrequency);
+                dict.setBigram(word, s.mWord, s.getProbability());
             }
         }
 
@@ -222,13 +222,13 @@
             if (null != word.mShortcutTargets) {
                 for (WeightedString target : word.mShortcutTargets) {
                     destination.write("  " + SHORTCUT_TAG + "=" + target.mWord + ","
-                            + FREQUENCY_TAG + "=" + target.mFrequency + "\n");
+                            + FREQUENCY_TAG + "=" + target.getProbability() + "\n");
                 }
             }
             if (null != word.mBigrams) {
                 for (WeightedString bigram : word.mBigrams) {
                     destination.write("  " + BIGRAM_TAG + "=" + bigram.mWord + ","
-                            + FREQUENCY_TAG + "=" + bigram.mFrequency + "\n");
+                            + FREQUENCY_TAG + "=" + bigram.getProbability() + "\n");
                 }
             }
         }
diff --git a/tools/dicttool/src/com/android/inputmethod/latin/dicttool/Diff.java b/tools/dicttool/src/com/android/inputmethod/latin/dicttool/Diff.java
index 7ac3c67..c9f6bd5 100644
--- a/tools/dicttool/src/com/android/inputmethod/latin/dicttool/Diff.java
+++ b/tools/dicttool/src/com/android/inputmethod/latin/dicttool/Diff.java
@@ -159,7 +159,7 @@
             if (null == list0) return false;
             for (final WeightedString attribute0 : list0) {
                 System.out.println(type + " removed: " + word + " " + attribute0.mWord + " "
-                        + attribute0.mFrequency);
+                        + attribute0.getProbability());
             }
             return true;
         }
@@ -175,8 +175,8 @@
                     for (final WeightedString attribute1 : list1) {
                         if (attribute0.mWord.equals(attribute1.mWord)) {
                             System.out.println(type + " freq changed: " + word + " "
-                                    + attribute0.mWord + " " + attribute0.mFrequency + " -> "
-                                    + attribute1.mFrequency);
+                                    + attribute0.mWord + " " + attribute0.getProbability() + " -> "
+                                    + attribute1.getProbability());
                             list1.remove(attribute1);
                             foundString = true;
                             break;
@@ -185,7 +185,7 @@
                     if (!foundString) {
                         // We come here if we haven't found any matching string.
                         System.out.println(type + " removed: " + word + " " + attribute0.mWord + " "
-                                + attribute0.mFrequency);
+                                + attribute0.getProbability());
                     }
                 } else {
                     list1.remove(attribute0);
@@ -197,7 +197,7 @@
         for (final WeightedString attribute1 : list1) {
             hasDifferences = true;
             System.out.println(type + " added: " + word + " " + attribute1.mWord + " "
-                    + attribute1.mFrequency);
+                    + attribute1.getProbability());
         }
         return hasDifferences;
     }
diff --git a/tools/dicttool/src/com/android/inputmethod/latin/dicttool/Info.java b/tools/dicttool/src/com/android/inputmethod/latin/dicttool/Info.java
index 350f427..8f17fcd 100644
--- a/tools/dicttool/src/com/android/inputmethod/latin/dicttool/Info.java
+++ b/tools/dicttool/src/com/android/inputmethod/latin/dicttool/Info.java
@@ -51,7 +51,8 @@
             if (null != w.mShortcutTargets) {
                 shortcutCount += w.mShortcutTargets.size();
                 for (WeightedString shortcutTarget : w.mShortcutTargets) {
-                    if (FormatSpec.SHORTCUT_WHITELIST_FREQUENCY == shortcutTarget.mFrequency) {
+                    if (FormatSpec.SHORTCUT_WHITELIST_FREQUENCY
+                            == shortcutTarget.getProbability()) {
                         ++whitelistCount;
                     }
                 }
@@ -84,8 +85,9 @@
         } else {
             for (final WeightedString shortcutTarget : shortcutTargets) {
                 System.out.println("  Shortcut target: " + shortcutTarget.mWord + " ("
-                        + (FormatSpec.SHORTCUT_WHITELIST_FREQUENCY == shortcutTarget.mFrequency
-                                ? "whitelist" : shortcutTarget.mFrequency) + ")");
+                        + (FormatSpec.SHORTCUT_WHITELIST_FREQUENCY
+                                == shortcutTarget.getProbability() ?
+                                        "whitelist" : shortcutTarget.getProbability()) + ")");
             }
         }
         final ArrayList<WeightedString> bigrams = ptNode.getBigrams();
@@ -93,7 +95,8 @@
             System.out.println("  No bigrams");
         } else {
             for (final WeightedString bigram : bigrams) {
-                System.out.println("  Bigram: " + bigram.mWord + " (" + bigram.mFrequency + ")");
+                System.out.println(
+                        "  Bigram: " + bigram.mWord + " (" + bigram.getProbability() + ")");
             }
         }
     }
diff --git a/tools/dicttool/src/com/android/inputmethod/latin/dicttool/XmlDictInputOutput.java b/tools/dicttool/src/com/android/inputmethod/latin/dicttool/XmlDictInputOutput.java
index d226251..cdc487b 100644
--- a/tools/dicttool/src/com/android/inputmethod/latin/dicttool/XmlDictInputOutput.java
+++ b/tools/dicttool/src/com/android/inputmethod/latin/dicttool/XmlDictInputOutput.java
@@ -319,7 +319,7 @@
             final ArrayList<WeightedString> bigramList = bigramMap.get(firstWord);
             for (final WeightedString bigram : bigramList) {
                 if (!dict.hasWord(bigram.mWord)) continue;
-                dict.setBigram(firstWord, bigram.mWord, bigram.mFrequency);
+                dict.setBigram(firstWord, bigram.mWord, bigram.getProbability());
             }
         }
         return dict;
@@ -369,7 +369,7 @@
                 destination.write("\n");
                 for (WeightedString target : word.mShortcutTargets) {
                     destination.write("    <" + SHORTCUT_TAG + " " + FREQUENCY_ATTR + "=\""
-                            + target.mFrequency + "\">" + target.mWord + "</" + SHORTCUT_TAG
+                            + target.getProbability() + "\">" + target.mWord + "</" + SHORTCUT_TAG
                             + ">\n");
                 }
                 destination.write("  ");
@@ -378,7 +378,8 @@
                 destination.write("\n");
                 for (WeightedString bigram : word.mBigrams) {
                     destination.write("    <" + BIGRAM_TAG + " " + FREQUENCY_ATTR + "=\""
-                            + bigram.mFrequency + "\">" + bigram.mWord + "</" + BIGRAM_TAG + ">\n");
+                            + bigram.getProbability() + "\">" + bigram.mWord
+                            + "</" + BIGRAM_TAG + ">\n");
                 }
                 destination.write("  ");
             }