diff --git a/java/src/com/android/inputmethod/latin/makedict/FormatSpec.java b/java/src/com/android/inputmethod/latin/makedict/FormatSpec.java
index 605930ab4..6d5827023 100644
--- a/java/src/com/android/inputmethod/latin/makedict/FormatSpec.java
+++ b/java/src/com/android/inputmethod/latin/makedict/FormatSpec.java
@@ -213,7 +213,6 @@ public final class FormatSpec {
     static final int SUPPORTS_DYNAMIC_UPDATE = 0x2;
     static final int FRENCH_LIGATURE_PROCESSING_FLAG = 0x4;
     static final int CONTAINS_BIGRAMS_FLAG = 0x8;
-    // TODO: Implement timestamps for unigram.
     static final int CONTAINS_TIMESTAMP_FLAG = 0x10;
 
     // TODO: Make this value adaptative to content data, store it in the header, and
@@ -267,6 +266,7 @@ public final class FormatSpec {
     // These values are used only by version 4 or later.
     static final String TRIE_FILE_EXTENSION = ".trie";
     static final String FREQ_FILE_EXTENSION = ".freq";
+    static final String UNIGRAM_TIMESTAMP_FILE_EXTENSION = ".timestamp";
     // tat = Terminal Address Table
     static final String TERMINAL_ADDRESS_TABLE_FILE_EXTENSION = ".tat";
     static final String BIGRAM_FILE_EXTENSION = ".bigram";
@@ -275,6 +275,7 @@ public final class FormatSpec {
     static final String CONTENT_TABLE_FILE_SUFFIX = "_index";
     static final int FREQUENCY_AND_FLAGS_SIZE = 2;
     static final int TERMINAL_ADDRESS_TABLE_ADDRESS_SIZE = 3;
+    static final int UNIGRAM_TIMESTAMP_SIZE = 4;
 
     // With the English main dictionary as of October 2013, the size of bigram address table is
     // is 584KB with the block size being 4.
diff --git a/java/src/com/android/inputmethod/latin/makedict/Ver4DictEncoder.java b/java/src/com/android/inputmethod/latin/makedict/Ver4DictEncoder.java
index fe9894246..5d5ab0462 100644
--- a/java/src/com/android/inputmethod/latin/makedict/Ver4DictEncoder.java
+++ b/java/src/com/android/inputmethod/latin/makedict/Ver4DictEncoder.java
@@ -45,6 +45,7 @@ public class Ver4DictEncoder implements DictEncoder {
     private int mHeaderSize;
     private OutputStream mTrieOutStream;
     private OutputStream mFreqOutStream;
+    private OutputStream mUnigramTimestampOutStream;
     private OutputStream mTerminalAddressTableOutStream;
     private File mDictDir;
     private String mBaseFilename;
@@ -238,18 +239,20 @@ public class Ver4DictEncoder implements DictEncoder {
         mDictDir = new File(mDictPlacedDir, mBaseFilename);
         final File trieFile = new File(mDictDir, mBaseFilename + FormatSpec.TRIE_FILE_EXTENSION);
         final File freqFile = new File(mDictDir, mBaseFilename + FormatSpec.FREQ_FILE_EXTENSION);
+        final File timestampFile = new File(mDictDir,
+                mBaseFilename + FormatSpec.UNIGRAM_TIMESTAMP_FILE_EXTENSION);
         final File terminalAddressTableFile = new File(mDictDir,
                 mBaseFilename + FormatSpec.TERMINAL_ADDRESS_TABLE_FILE_EXTENSION);
         if (!mDictDir.isDirectory()) {
             if (mDictDir.exists()) mDictDir.delete();
             mDictDir.mkdirs();
         }
-        if (!trieFile.exists()) trieFile.createNewFile();
-        if (!freqFile.exists()) freqFile.createNewFile();
-        if (!terminalAddressTableFile.exists()) terminalAddressTableFile.createNewFile();
         mTrieOutStream = new FileOutputStream(trieFile);
         mFreqOutStream = new FileOutputStream(freqFile);
         mTerminalAddressTableOutStream = new FileOutputStream(terminalAddressTableFile);
+        if (formatOptions.mHasTimestamp) {
+            mUnigramTimestampOutStream = new FileOutputStream(timestampFile);
+        }
     }
 
     private void close() throws IOException {
@@ -263,6 +266,9 @@ public class Ver4DictEncoder implements DictEncoder {
             if (mTerminalAddressTableOutStream != null) {
                 mTerminalAddressTableOutStream.close();
             }
+            if (mUnigramTimestampOutStream != null) {
+                mUnigramTimestampOutStream.close();
+            }
         } finally {
             mTrieOutStream = null;
             mFreqOutStream = null;
@@ -302,6 +308,9 @@ public class Ver4DictEncoder implements DictEncoder {
         if (MakedictLog.DBG) BinaryDictEncoderUtils.checkFlatPtNodeArrayList(flatNodes);
 
         writeTerminalData(flatNodes, terminalCount);
+        if (formatOptions.mHasTimestamp) {
+            initUnigramTimestamps(terminalCount);
+        }
         mBigramWriter = new BigramContentWriter(mBaseFilename, terminalCount, mDictDir,
                 formatOptions.mHasTimestamp);
         writeBigrams(flatNodes, dict);
@@ -454,4 +463,11 @@ public class Ver4DictEncoder implements DictEncoder {
         mFreqOutStream.write(freqBuf);
         mTerminalAddressTableOutStream.write(terminalAddressTableBuf);
     }
+
+    private void initUnigramTimestamps(final int terminalCount) throws IOException {
+        // Initial value of time stamps for each word is 0.
+        final byte[] unigramTimestampBuf =
+                new byte[terminalCount * FormatSpec.UNIGRAM_TIMESTAMP_SIZE];
+        mUnigramTimestampOutStream.write(unigramTimestampBuf);
+    }
 }