diff --git a/java/src/com/android/inputmethod/latin/DictionaryFactory.java b/java/src/com/android/inputmethod/latin/DictionaryFactory.java
index 3721132..828e54f 100644
--- a/java/src/com/android/inputmethod/latin/DictionaryFactory.java
+++ b/java/src/com/android/inputmethod/latin/DictionaryFactory.java
@@ -51,7 +51,7 @@
         if (null == locale) {
             Log.e(TAG, "No locale defined for dictionary");
             return new DictionaryCollection(Dictionary.TYPE_MAIN,
-                    createBinaryDictionary(context, locale));
+                    createReadOnlyBinaryDictionary(context, locale));
         }
 
         final LinkedList<Dictionary> dictList = CollectionUtils.newLinkedList();
@@ -59,11 +59,11 @@
                 BinaryDictionaryGetter.getDictionaryFiles(locale, context);
         if (null != assetFileList) {
             for (final AssetFileAddress f : assetFileList) {
-                final BinaryDictionary binaryDictionary = new BinaryDictionary(f.mFilename,
-                        f.mOffset, f.mLength, useFullEditDistance, locale, Dictionary.TYPE_MAIN,
-                        false /* isUpdatable */);
-                if (binaryDictionary.isValidDictionary()) {
-                    dictList.add(binaryDictionary);
+                final ReadOnlyBinaryDictionary readOnlyBinaryDictionary =
+                        new ReadOnlyBinaryDictionary(f.mFilename, f.mOffset, f.mLength,
+                                useFullEditDistance, locale, Dictionary.TYPE_MAIN);
+                if (readOnlyBinaryDictionary.isValidDictionary()) {
+                    dictList.add(readOnlyBinaryDictionary);
                 }
             }
         }
@@ -89,12 +89,12 @@
     }
 
     /**
-     * Initializes a dictionary from a raw resource file
+     * Initializes a read-only binary dictionary from a raw resource file
      * @param context application context for reading resources
      * @param locale the locale to use for the resource
-     * @return an initialized instance of BinaryDictionary
+     * @return an initialized instance of ReadOnlyBinaryDictionary
      */
-    protected static BinaryDictionary createBinaryDictionary(final Context context,
+    protected static ReadOnlyBinaryDictionary createReadOnlyBinaryDictionary(final Context context,
             final Locale locale) {
         AssetFileDescriptor afd = null;
         try {
@@ -113,9 +113,8 @@
                 Log.e(TAG, "sourceDir is not a file: " + sourceDir);
                 return null;
             }
-            return new BinaryDictionary(sourceDir, afd.getStartOffset(), afd.getLength(),
-                    false /* useFullEditDistance */, locale, Dictionary.TYPE_MAIN,
-                    false /* isUpdatable */);
+            return new ReadOnlyBinaryDictionary(sourceDir, afd.getStartOffset(), afd.getLength(),
+                    false /* useFullEditDistance */, locale, Dictionary.TYPE_MAIN);
         } catch (android.content.res.Resources.NotFoundException e) {
             Log.e(TAG, "Could not find the resource");
             return null;
@@ -142,10 +141,10 @@
         final DictionaryCollection dictionaryCollection =
                 new DictionaryCollection(Dictionary.TYPE_MAIN);
         for (final AssetFileAddress address : dictionaryList) {
-            final BinaryDictionary binaryDictionary = new BinaryDictionary(address.mFilename,
-                    address.mOffset, address.mLength, useFullEditDistance, locale,
-                    Dictionary.TYPE_MAIN, false /* isUpdatable */);
-            dictionaryCollection.addDictionary(binaryDictionary);
+            final ReadOnlyBinaryDictionary readOnlyBinaryDictionary = new ReadOnlyBinaryDictionary(
+                    address.mFilename, address.mOffset, address.mLength, useFullEditDistance,
+                    locale, Dictionary.TYPE_MAIN);
+            dictionaryCollection.addDictionary(readOnlyBinaryDictionary);
         }
         return dictionaryCollection;
     }
diff --git a/java/src/com/android/inputmethod/latin/ReadOnlyBinaryDictionary.java b/java/src/com/android/inputmethod/latin/ReadOnlyBinaryDictionary.java
new file mode 100644
index 0000000..68505ce
--- /dev/null
+++ b/java/src/com/android/inputmethod/latin/ReadOnlyBinaryDictionary.java
@@ -0,0 +1,120 @@
+/*
+ * Copyright (C) 2013 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.inputmethod.latin;
+
+import com.android.inputmethod.keyboard.ProximityInfo;
+import com.android.inputmethod.latin.SuggestedWords.SuggestedWordInfo;
+
+import java.util.ArrayList;
+import java.util.Locale;
+import java.util.concurrent.locks.ReentrantReadWriteLock;
+
+/**
+ * This class provides binary dictionary reading operations with locking. An instance of this class
+ * can be used by multiple threads. Note that different session IDs must be used when multiple
+ * threads get suggestions using this class.
+ */
+public final class ReadOnlyBinaryDictionary extends Dictionary {
+    /**
+     * A lock for accessing binary dictionary. Only closing binary dictionary is the operation
+     * that change the state of dictionary.
+     */
+    private final ReentrantReadWriteLock mLock = new ReentrantReadWriteLock();
+
+    private final BinaryDictionary mBinaryDictionary;
+
+    public ReadOnlyBinaryDictionary(final String filename, final long offset, final long length,
+            final boolean useFullEditDistance, final Locale locale, final String dictType) {
+        super(dictType);
+        mBinaryDictionary = new BinaryDictionary(filename, offset, length, useFullEditDistance,
+                locale, dictType, false /* isUpdatable */);
+    }
+
+    public boolean isValidDictionary() {
+        return mBinaryDictionary.isValidDictionary();
+    }
+
+    @Override
+    public ArrayList<SuggestedWordInfo> getSuggestions(final WordComposer composer,
+            final String prevWord, final ProximityInfo proximityInfo,
+            final boolean blockOffensiveWords, final int[] additionalFeaturesOptions) {
+        return getSuggestionsWithSessionId(composer, prevWord, proximityInfo, blockOffensiveWords,
+                additionalFeaturesOptions, 0 /* sessionId */);
+    }
+
+    @Override
+    public ArrayList<SuggestedWordInfo> getSuggestionsWithSessionId(final WordComposer composer,
+            final String prevWord, final ProximityInfo proximityInfo,
+            final boolean blockOffensiveWords, final int[] additionalFeaturesOptions,
+            final int sessionId) {
+        if (mLock.readLock().tryLock()) {
+            try {
+                return mBinaryDictionary.getSuggestions(composer, prevWord, proximityInfo,
+                        blockOffensiveWords, additionalFeaturesOptions);
+            } finally {
+                mLock.readLock().unlock();
+            }
+        }
+        return null;
+    }
+
+    @Override
+    public boolean isValidWord(final String word) {
+        if (mLock.readLock().tryLock()) {
+            try {
+                return mBinaryDictionary.isValidWord(word);
+            } finally {
+                mLock.readLock().unlock();
+            }
+        }
+        return false;
+    }
+
+    @Override
+    public boolean shouldAutoCommit(final SuggestedWordInfo candidate) {
+        if (mLock.readLock().tryLock()) {
+            try {
+                return mBinaryDictionary.shouldAutoCommit(candidate);
+            } finally {
+                mLock.readLock().unlock();
+            }
+        }
+        return false;
+    }
+
+    @Override
+    public int getFrequency(final String word) {
+        if (mLock.readLock().tryLock()) {
+            try {
+                return mBinaryDictionary.getFrequency(word);
+            } finally {
+                mLock.readLock().unlock();
+            }
+        }
+        return NOT_A_PROBABILITY;
+    }
+
+    @Override
+    public void close() {
+        mLock.writeLock().lock();
+        try {
+            mBinaryDictionary.close();
+        } finally {
+            mLock.writeLock().unlock();
+        }
+    }
+}