diff --git a/java/src/com/android/inputmethod/latin/ExpandableBinaryDictionary.java b/java/src/com/android/inputmethod/latin/ExpandableBinaryDictionary.java
index 3f11391..b481371 100644
--- a/java/src/com/android/inputmethod/latin/ExpandableBinaryDictionary.java
+++ b/java/src/com/android/inputmethod/latin/ExpandableBinaryDictionary.java
@@ -84,6 +84,9 @@
     /** Controls access to the local binary dictionary for this instance. */
     private final DictionaryController mLocalDictionaryController = new DictionaryController();
 
+    /* A extension for a binary dictionary file. */
+    public static final String DICT_FILE_EXTENSION = ".dict";
+
     /**
      * Abstract method for loading the unigrams and bigrams of a given dictionary in a background
      * thread.
@@ -129,7 +132,7 @@
     }
 
     protected static String getFilenameWithLocale(final String name, final String localeStr) {
-        return name + "." + localeStr + ".dict";
+        return name + "." + localeStr + DICT_FILE_EXTENSION;
     }
 
     /**
diff --git a/java/src/com/android/inputmethod/latin/personalization/PersonalizationPredictionDictionary.java b/java/src/com/android/inputmethod/latin/personalization/PersonalizationPredictionDictionary.java
index 955bd27..a038d0a 100644
--- a/java/src/com/android/inputmethod/latin/personalization/PersonalizationPredictionDictionary.java
+++ b/java/src/com/android/inputmethod/latin/personalization/PersonalizationPredictionDictionary.java
@@ -17,6 +17,7 @@
 package com.android.inputmethod.latin.personalization;
 
 import com.android.inputmethod.latin.Dictionary;
+import com.android.inputmethod.latin.ExpandableBinaryDictionary;
 
 import android.content.Context;
 import android.content.SharedPreferences;
@@ -31,6 +32,6 @@
 
     @Override
     protected String getDictionaryFileName() {
-        return NAME + "." + getLocale() + ".dict";
+        return NAME + "." + getLocale() + ExpandableBinaryDictionary.DICT_FILE_EXTENSION;
     }
 }
diff --git a/java/src/com/android/inputmethod/latin/personalization/UserHistoryPredictionDictionary.java b/java/src/com/android/inputmethod/latin/personalization/UserHistoryPredictionDictionary.java
index b8db75f..76e48c7 100644
--- a/java/src/com/android/inputmethod/latin/personalization/UserHistoryPredictionDictionary.java
+++ b/java/src/com/android/inputmethod/latin/personalization/UserHistoryPredictionDictionary.java
@@ -17,6 +17,7 @@
 package com.android.inputmethod.latin.personalization;
 
 import com.android.inputmethod.latin.Dictionary;
+import com.android.inputmethod.latin.ExpandableBinaryDictionary;
 
 import android.content.Context;
 import android.content.SharedPreferences;
@@ -35,6 +36,6 @@
 
     @Override
     protected String getDictionaryFileName() {
-        return NAME + "." + getLocale() + ".dict";
+        return NAME + "." + getLocale() + ExpandableBinaryDictionary.DICT_FILE_EXTENSION;
     }
 }
diff --git a/tests/src/com/android/inputmethod/latin/makedict/BinaryDictDecoderEncoderTests.java b/tests/src/com/android/inputmethod/latin/makedict/BinaryDictDecoderEncoderTests.java
index e98790b..70c77e4 100644
--- a/tests/src/com/android/inputmethod/latin/makedict/BinaryDictDecoderEncoderTests.java
+++ b/tests/src/com/android/inputmethod/latin/makedict/BinaryDictDecoderEncoderTests.java
@@ -71,6 +71,8 @@
     private static final FormatSpec.FormatOptions VERSION3_WITH_DYNAMIC_UPDATE =
             new FormatSpec.FormatOptions(3, true /* supportsDynamicUpdate */);
 
+    private static final String TEST_DICT_FILE_EXTENSION = ".testDict";
+
     public BinaryDictDecoderEncoderTests() {
         this(System.currentTimeMillis(), DEFAULT_MAX_UNIGRAMS);
     }
@@ -293,7 +295,8 @@
             final String message) {
         File file = null;
         try {
-            file = File.createTempFile("runReadAndWrite", ".dict", getContext().getCacheDir());
+            file = File.createTempFile("runReadAndWrite", TEST_DICT_FILE_EXTENSION,
+                    getContext().getCacheDir());
         } catch (IOException e) {
             Log.e(TAG, "IOException", e);
         }
@@ -435,7 +438,8 @@
             final FormatSpec.FormatOptions formatOptions, final String message) {
         File file = null;
         try {
-            file = File.createTempFile("runReadUnigrams", ".dict", getContext().getCacheDir());
+            file = File.createTempFile("runReadUnigrams", TEST_DICT_FILE_EXTENSION,
+                    getContext().getCacheDir());
         } catch (IOException e) {
             Log.e(TAG, "IOException", e);
         }
@@ -533,7 +537,7 @@
     public void testGetTerminalPosition() {
         File file = null;
         try {
-            file = File.createTempFile("testGetTerminalPosition", ".dict",
+            file = File.createTempFile("testGetTerminalPosition", TEST_DICT_FILE_EXTENSION,
                     getContext().getCacheDir());
         } catch (IOException e) {
             // do nothing
@@ -593,7 +597,8 @@
     public void testDeleteWord() {
         File file = null;
         try {
-            file = File.createTempFile("testDeleteWord", ".dict", getContext().getCacheDir());
+            file = File.createTempFile("testDeleteWord", TEST_DICT_FILE_EXTENSION,
+                    getContext().getCacheDir());
         } catch (IOException e) {
             // do nothing
         }
diff --git a/tests/src/com/android/inputmethod/latin/makedict/BinaryDictIOUtilsTests.java b/tests/src/com/android/inputmethod/latin/makedict/BinaryDictIOUtilsTests.java
index 300fd6a..e9119f0 100644
--- a/tests/src/com/android/inputmethod/latin/makedict/BinaryDictIOUtilsTests.java
+++ b/tests/src/com/android/inputmethod/latin/makedict/BinaryDictIOUtilsTests.java
@@ -48,6 +48,8 @@
     public static final int DEFAULT_MAX_UNIGRAMS = 1500;
     private final int mMaxUnigrams;
 
+    private static final String TEST_DICT_FILE_EXTENSION = ".testDict";
+
     private static final String[] CHARACTERS = {
         "a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m",
         "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z",
@@ -234,7 +236,8 @@
     public void testInsertWord() {
         File file = null;
         try {
-            file = File.createTempFile("testInsertWord", ".dict", getContext().getCacheDir());
+            file = File.createTempFile("testInsertWord", TEST_DICT_FILE_EXTENSION,
+                    getContext().getCacheDir());
         } catch (IOException e) {
             fail("IOException while creating temporary file: " + e);
         }
@@ -284,7 +287,7 @@
     public void testInsertWordWithBigrams() {
         File file = null;
         try {
-            file = File.createTempFile("testInsertWordWithBigrams", ".dict",
+            file = File.createTempFile("testInsertWordWithBigrams", TEST_DICT_FILE_EXTENSION,
                     getContext().getCacheDir());
         } catch (IOException e) {
             fail("IOException while creating temporary file: " + e);
@@ -322,7 +325,8 @@
     public void testRandomWords() {
         File file = null;
         try {
-            file = File.createTempFile("testRandomWord", ".dict", getContext().getCacheDir());
+            file = File.createTempFile("testRandomWord", TEST_DICT_FILE_EXTENSION,
+                    getContext().getCacheDir());
         } catch (IOException e) {
         }
         assertNotNull(file);
diff --git a/tests/src/com/android/inputmethod/latin/personalization/UserHistoryDictionaryTests.java b/tests/src/com/android/inputmethod/latin/personalization/UserHistoryDictionaryTests.java
index c2a6264..304b792 100644
--- a/tests/src/com/android/inputmethod/latin/personalization/UserHistoryDictionaryTests.java
+++ b/tests/src/com/android/inputmethod/latin/personalization/UserHistoryDictionaryTests.java
@@ -22,6 +22,7 @@
 import android.test.suitebuilder.annotation.LargeTest;
 import android.util.Log;
 
+import com.android.inputmethod.latin.ExpandableBinaryDictionary;
 import com.android.inputmethod.latin.utils.CollectionUtils;
 
 import java.io.File;
@@ -81,12 +82,12 @@
         }
     }
 
-    private void addAndWriteRandomWords(final String locale, final int numberOfWords,
+    private void addAndWriteRandomWords(final String testFilenameSuffix, final int numberOfWords,
             final Random random) {
         final List<String> words = generateWords(numberOfWords, random);
         final UserHistoryPredictionDictionary dict =
                 PersonalizationDictionaryHelper.getUserHistoryPredictionDictionary(getContext(),
-                        locale, mPrefs);
+                        testFilenameSuffix /* locale */, mPrefs);
         // Add random words to the user history dictionary.
         addToDict(dict, words);
         // write to file.
@@ -97,12 +98,12 @@
         File dictFile = null;
         Log.d(TAG, "This test can be used for profiling.");
         Log.d(TAG, "Usage: please set UserHistoryDictionary.PROFILE_SAVE_RESTORE to true.");
-        final String locale = "testRandomWords" + System.currentTimeMillis();
+        final String testFilenameSuffix = "testRandomWords" + System.currentTimeMillis();
         final int numberOfWords = 1000;
         final Random random = new Random(123456);
 
         try {
-            addAndWriteRandomWords(locale, numberOfWords, random);
+            addAndWriteRandomWords(testFilenameSuffix, numberOfWords, random);
         } finally {
             try {
                 Log.d(TAG, "waiting for writing ...");
@@ -111,7 +112,8 @@
                 Log.d(TAG, "InterruptedException: " + e);
             }
 
-            final String fileName = UserHistoryPredictionDictionary.NAME + "." + locale + ".dict";
+            final String fileName = UserHistoryPredictionDictionary.NAME + "." + testFilenameSuffix
+                    + ExpandableBinaryDictionary.DICT_FILE_EXTENSION;
             dictFile = new File(getContext().getFilesDir(), fileName);
 
             if (dictFile != null) {
@@ -135,8 +137,8 @@
             String testFilenameSuffixes[] = new String[numberOfLanguages];
             for (int i = 0; i < numberOfLanguages; i++) {
                 testFilenameSuffixes[i] = "testSwitchingLanguages" + i;
-                final String fileName = "UserHistoryDictionary." + testFilenameSuffixes[i]
-                        + ".dict";
+                final String fileName = UserHistoryPredictionDictionary.NAME + "." +
+                        testFilenameSuffixes[i] + ExpandableBinaryDictionary.DICT_FILE_EXTENSION;
                 dictFiles[i] = new File(getContext().getFilesDir(), fileName);
             }
 
diff --git a/tests/src/com/android/inputmethod/latin/utils/UserHistoryDictIOUtilsTests.java b/tests/src/com/android/inputmethod/latin/utils/UserHistoryDictIOUtilsTests.java
index fd55176..8f5bec8 100644
--- a/tests/src/com/android/inputmethod/latin/utils/UserHistoryDictIOUtilsTests.java
+++ b/tests/src/com/android/inputmethod/latin/utils/UserHistoryDictIOUtilsTests.java
@@ -49,6 +49,7 @@
     private static final int BIGRAM_FREQUENCY = 100;
     private static final ArrayList<String> NOT_HAVE_BIGRAM = new ArrayList<String>();
     private static final FormatSpec.FormatOptions FORMAT_OPTIONS = new FormatSpec.FormatOptions(2);
+    private static final String TEST_DICT_FILE_EXTENSION = ".testDict";
 
     /**
      * Return same frequency for all words and bigrams
@@ -177,7 +178,8 @@
 
         File file = null;
         try {
-            file = File.createTempFile("testReadAndWrite", ".dict", getContext().getCacheDir());
+            file = File.createTempFile("testReadAndWrite", TEST_DICT_FILE_EXTENSION,
+                    getContext().getCacheDir());
         } catch (IOException e) {
             Log.d(TAG, "IOException while creating a temporary file", e);
         }