diff --git a/java/src/com/android/inputmethod/latin/makedict/AbstractDictDecoder.java b/java/src/com/android/inputmethod/latin/makedict/AbstractDictDecoder.java
index fda97da..b75fc37 100644
--- a/java/src/com/android/inputmethod/latin/makedict/AbstractDictDecoder.java
+++ b/java/src/com/android/inputmethod/latin/makedict/AbstractDictDecoder.java
@@ -32,6 +32,10 @@
  * A base class of the binary dictionary decoder.
  */
 public abstract class AbstractDictDecoder implements DictDecoder {
+    private static final int SUCCESS = 0;
+    private static final int ERROR_CANNOT_READ = 1;
+    private static final int ERROR_WRONG_FORMAT = 2;
+
     protected FileHeader readHeader(final DictBuffer dictBuffer)
             throws IOException, UnsupportedFormatException {
         if (dictBuffer == null) {
@@ -204,4 +208,25 @@
             return readLength;
         }
     }
+
+    /**
+     * Check whether the header contains the expected information. This is a no-error method,
+     * that will return an error code and never throw a checked exception.
+     * @return an error code, either ERROR_* or SUCCESS.
+     */
+    private int checkHeader() {
+        try {
+            readHeader();
+        } catch (IOException e) {
+            return ERROR_CANNOT_READ;
+        } catch (UnsupportedFormatException e) {
+            return ERROR_WRONG_FORMAT;
+        }
+        return SUCCESS;
+    }
+
+    @Override
+    public boolean hasValidRawBinaryDictionary() {
+        return checkHeader() == SUCCESS;
+    }
 }
diff --git a/java/src/com/android/inputmethod/latin/makedict/BinaryDictDecoderUtils.java b/java/src/com/android/inputmethod/latin/makedict/BinaryDictDecoderUtils.java
index 8a8ceaa..17c609f 100644
--- a/java/src/com/android/inputmethod/latin/makedict/BinaryDictDecoderUtils.java
+++ b/java/src/com/android/inputmethod/latin/makedict/BinaryDictDecoderUtils.java
@@ -24,12 +24,9 @@
 import com.android.inputmethod.latin.makedict.FusionDictionary.WeightedString;
 
 import java.io.File;
-import java.io.FileInputStream;
-import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.io.OutputStream;
 import java.nio.ByteBuffer;
-import java.nio.channels.FileChannel;
 import java.util.ArrayList;
 import java.util.Map;
 import java.util.TreeMap;
@@ -639,32 +636,10 @@
     /**
      * Basic test to find out whether the file is a binary dictionary or not.
      *
-     * Concretely this only tests the magic number.
-     *
      * @param file The file to test.
      * @return true if it's a binary dictionary, false otherwise
      */
     public static boolean isBinaryDictionary(final File file) {
-        FileInputStream inStream = null;
-        try {
-            inStream = new FileInputStream(file);
-            final ByteBuffer buffer = inStream.getChannel().map(
-                    FileChannel.MapMode.READ_ONLY, 0, file.length());
-            final int version = getFormatVersion(new ByteBufferDictBuffer(buffer));
-            return (version >= FormatSpec.MINIMUM_SUPPORTED_VERSION
-                    && version <= FormatSpec.MAXIMUM_SUPPORTED_VERSION);
-        } catch (FileNotFoundException e) {
-            return false;
-        } catch (IOException e) {
-            return false;
-        } finally {
-            if (inStream != null) {
-                try {
-                    inStream.close();
-                } catch (IOException e) {
-                    // do nothing
-                }
-            }
-        }
+        return FormatSpec.getDictDecoder(file).hasValidRawBinaryDictionary();
     }
 }
diff --git a/java/src/com/android/inputmethod/latin/makedict/DictDecoder.java b/java/src/com/android/inputmethod/latin/makedict/DictDecoder.java
index 9154398..b4838f0 100644
--- a/java/src/com/android/inputmethod/latin/makedict/DictDecoder.java
+++ b/java/src/com/android/inputmethod/latin/makedict/DictDecoder.java
@@ -128,7 +128,8 @@
      * Opens the dictionary file and makes DictBuffer.
      */
     @UsedForTesting
-    public void openDictBuffer() throws FileNotFoundException, IOException;
+    public void openDictBuffer() throws FileNotFoundException, IOException,
+            UnsupportedFormatException;
     @UsedForTesting
     public boolean isDictBufferOpen();
 
@@ -229,4 +230,9 @@
     }
 
     public void skipPtNode(final FormatOptions formatOptions);
+
+    /**
+     * @return whether this decoder has a valid binary dictionary that it can decode.
+     */
+    public boolean hasValidRawBinaryDictionary();
 }
diff --git a/java/src/com/android/inputmethod/latin/makedict/Ver4DictDecoder.java b/java/src/com/android/inputmethod/latin/makedict/Ver4DictDecoder.java
index f0fed3f..8833c35 100644
--- a/java/src/com/android/inputmethod/latin/makedict/Ver4DictDecoder.java
+++ b/java/src/com/android/inputmethod/latin/makedict/Ver4DictDecoder.java
@@ -103,7 +103,7 @@
         mDictBuffer = mFrequencyBuffer = null;
     }
 
-    protected File getFile(final int fileType) {
+    protected File getFile(final int fileType) throws UnsupportedFormatException {
         if (fileType == FILETYPE_TRIE) {
             return new File(mDictDirectory,
                     mDictDirectory.getName() + FormatSpec.TRIE_FILE_EXTENSION);
@@ -122,12 +122,16 @@
                     mDictDirectory.getName() + FormatSpec.SHORTCUT_FILE_EXTENSION
                             + FormatSpec.SHORTCUT_CONTENT_ID);
         } else {
-            throw new RuntimeException("Unsupported kind of file : " + fileType);
+            throw new UnsupportedFormatException("Unsupported kind of file : " + fileType);
         }
     }
 
     @Override
-    public void openDictBuffer() throws FileNotFoundException, IOException {
+    public void openDictBuffer() throws FileNotFoundException, IOException,
+            UnsupportedFormatException {
+        if (!mDictDirectory.isDirectory()) {
+            throw new UnsupportedFormatException("Format 4 dictionary needs a directory");
+        }
         mDictBuffer = mBufferFactory.getDictionaryBuffer(getFile(FILETYPE_TRIE));
         mFrequencyBuffer = mBufferFactory.getDictionaryBuffer(getFile(FILETYPE_FREQUENCY));
         mTerminalAddressTableBuffer = mBufferFactory.getDictionaryBuffer(
diff --git a/java/src/com/android/inputmethod/latin/makedict/Ver4DictUpdater.java b/java/src/com/android/inputmethod/latin/makedict/Ver4DictUpdater.java
index 65860ee..883709f 100644
--- a/java/src/com/android/inputmethod/latin/makedict/Ver4DictUpdater.java
+++ b/java/src/com/android/inputmethod/latin/makedict/Ver4DictUpdater.java
@@ -45,7 +45,8 @@
     private final File mFrequencyFile;
 
     @UsedForTesting
-    public Ver4DictUpdater(final File dictDirectory, final int factoryType) {
+    public Ver4DictUpdater(final File dictDirectory, final int factoryType)
+            throws UnsupportedFormatException {
         // DictUpdater must have an updatable DictBuffer.
         super(dictDirectory, ((factoryType & MASK_DICTBUFFER) == USE_BYTEARRAY)
                 ? USE_BYTEARRAY : USE_WRITABLE_BYTEBUFFER);
@@ -664,7 +665,8 @@
         frequencyStream.close();
     }
 
-    private void insertTerminalPosition(final int posOfTerminal) throws IOException {
+    private void insertTerminalPosition(final int posOfTerminal) throws IOException,
+            UnsupportedFormatException {
         final OutputStream terminalPosStream = new FileOutputStream(
                 getFile(FILETYPE_TERMINAL_ADDRESS_TABLE), true /* append */);
         BinaryDictEncoderUtils.writeUIntToStream(terminalPosStream, posOfTerminal,
@@ -702,7 +704,7 @@
         updater.insertShortcuts(terminalId, shortcuts);
     }
 
-    private void openBuffersAndStream() throws IOException {
+    private void openBuffersAndStream() throws IOException, UnsupportedFormatException {
         openDictBuffer();
         mDictStream = new FileOutputStream(getFile(FILETYPE_TRIE), true /* append */);
     }
diff --git a/java/src/com/android/inputmethod/latin/personalization/DecayingExpandableBinaryDictionaryBase.java b/java/src/com/android/inputmethod/latin/personalization/DecayingExpandableBinaryDictionaryBase.java
index 8b94883..5edac23 100644
--- a/java/src/com/android/inputmethod/latin/personalization/DecayingExpandableBinaryDictionaryBase.java
+++ b/java/src/com/android/inputmethod/latin/personalization/DecayingExpandableBinaryDictionaryBase.java
@@ -28,6 +28,7 @@
 import com.android.inputmethod.latin.LatinImeLogger;
 import com.android.inputmethod.latin.makedict.DictDecoder;
 import com.android.inputmethod.latin.makedict.FormatSpec;
+import com.android.inputmethod.latin.makedict.UnsupportedFormatException;
 import com.android.inputmethod.latin.settings.Settings;
 import com.android.inputmethod.latin.utils.CollectionUtils;
 import com.android.inputmethod.latin.utils.UserHistoryDictIOUtils;
@@ -222,6 +223,8 @@
             UserHistoryDictIOUtils.readDictionaryBinary(dictDecoder, listener);
         } catch (IOException e) {
             Log.d(TAG, "IOException on opening a bytebuffer", e);
+        } catch (UnsupportedFormatException e) {
+            Log.d(TAG, "Unsupported format, can't read the dictionary", e);
         } finally {
             if (PROFILE_SAVE_RESTORE) {
                 final long diff = System.currentTimeMillis() - now;
@@ -291,6 +294,8 @@
             UserHistoryDictIOUtils.readDictionaryBinary(dictDecoder, listener);
         } catch (IOException e) {
             Log.d(TAG, "IOException on opening a bytebuffer", e);
+        } catch (UnsupportedFormatException e) {
+            Log.d(TAG, "Unsupported format, can't read the dictionary", e);
         }
     }
 
diff --git a/tests/src/com/android/inputmethod/latin/makedict/BinaryDictDecoderEncoderTests.java b/tests/src/com/android/inputmethod/latin/makedict/BinaryDictDecoderEncoderTests.java
index 48d36b6..c4749df 100644
--- a/tests/src/com/android/inputmethod/latin/makedict/BinaryDictDecoderEncoderTests.java
+++ b/tests/src/com/android/inputmethod/latin/makedict/BinaryDictDecoderEncoderTests.java
@@ -29,6 +29,7 @@
 import com.android.inputmethod.latin.makedict.FusionDictionary.PtNode;
 import com.android.inputmethod.latin.makedict.FusionDictionary.PtNodeArray;
 import com.android.inputmethod.latin.makedict.FusionDictionary.WeightedString;
+import com.android.inputmethod.latin.makedict.UnsupportedFormatException;
 import com.android.inputmethod.latin.utils.ByteArrayDictBuffer;
 import com.android.inputmethod.latin.utils.CollectionUtils;
 
@@ -563,7 +564,8 @@
         try {
             dictDecoder.openDictBuffer();
         } catch (IOException e) {
-            // ignore
+            Log.e(TAG, "IOException while opening the buffer", e);
+        } catch (UnsupportedFormatException e) {
             Log.e(TAG, "IOException while opening the buffer", e);
         }
         assertTrue("Can't get the buffer", dictDecoder.isDictBufferOpen());
@@ -639,7 +641,8 @@
         }
     }
 
-    private void runTestDeleteWord(final FormatOptions formatOptions) {
+    private void runTestDeleteWord(final FormatOptions formatOptions)
+            throws IOException, UnsupportedFormatException {
         final String dictName = "testDeleteWord";
         final String dictVersion = Long.toString(System.currentTimeMillis());
         final File file = BinaryDictUtils.getDictFile(dictName, dictVersion, formatOptions,
@@ -652,25 +655,20 @@
         timeWritingDictToFile(file, dict, formatOptions);
 
         final DictUpdater dictUpdater = BinaryDictUtils.getDictUpdater(file, formatOptions);
+        MoreAsserts.assertNotEqual(FormatSpec.NOT_VALID_WORD,
+                dictUpdater.getTerminalPosition(sWords.get(0)));
+        dictUpdater.deleteWord(sWords.get(0));
+        assertEquals(FormatSpec.NOT_VALID_WORD,
+                dictUpdater.getTerminalPosition(sWords.get(0)));
 
-        try {
-            MoreAsserts.assertNotEqual(FormatSpec.NOT_VALID_WORD,
-                    dictUpdater.getTerminalPosition(sWords.get(0)));
-            dictUpdater.deleteWord(sWords.get(0));
-            assertEquals(FormatSpec.NOT_VALID_WORD,
-                    dictUpdater.getTerminalPosition(sWords.get(0)));
-
-            MoreAsserts.assertNotEqual(FormatSpec.NOT_VALID_WORD,
-                    dictUpdater.getTerminalPosition(sWords.get(5)));
-            dictUpdater.deleteWord(sWords.get(5));
-            assertEquals(FormatSpec.NOT_VALID_WORD,
-                    dictUpdater.getTerminalPosition(sWords.get(5)));
-        } catch (IOException e) {
-        } catch (UnsupportedFormatException e) {
-        }
+        MoreAsserts.assertNotEqual(FormatSpec.NOT_VALID_WORD,
+                dictUpdater.getTerminalPosition(sWords.get(5)));
+        dictUpdater.deleteWord(sWords.get(5));
+        assertEquals(FormatSpec.NOT_VALID_WORD,
+                dictUpdater.getTerminalPosition(sWords.get(5)));
     }
 
-    public void testDeleteWord() {
+    public void testDeleteWord() throws IOException, UnsupportedFormatException {
         runTestDeleteWord(BinaryDictUtils.VERSION3_WITH_DYNAMIC_UPDATE);
         runTestDeleteWord(BinaryDictUtils.VERSION4_WITH_DYNAMIC_UPDATE);
     }
diff --git a/tests/src/com/android/inputmethod/latin/makedict/BinaryDictUtils.java b/tests/src/com/android/inputmethod/latin/makedict/BinaryDictUtils.java
index f476738..5ec3725 100644
--- a/tests/src/com/android/inputmethod/latin/makedict/BinaryDictUtils.java
+++ b/tests/src/com/android/inputmethod/latin/makedict/BinaryDictUtils.java
@@ -73,13 +73,14 @@
         }
     }
 
-    public static DictUpdater getDictUpdater(final File file, final FormatOptions formatOptions) {
+    public static DictUpdater getDictUpdater(final File file, final FormatOptions formatOptions)
+            throws UnsupportedFormatException {
         if (formatOptions.mVersion == FormatSpec.VERSION4) {
             return new Ver4DictUpdater(file, DictDecoder.USE_WRITABLE_BYTEBUFFER);
         } else if (formatOptions.mVersion == 3) {
             return new Ver3DictUpdater(file, DictDecoder.USE_WRITABLE_BYTEBUFFER);
         } else {
-            throw new RuntimeException("The format option has a wrong version : "
+            throw new UnsupportedFormatException("The format option has a wrong version : "
                     + formatOptions.mVersion);
         }
     }
diff --git a/tests/src/com/android/inputmethod/latin/utils/UserHistoryDictIOUtilsTests.java b/tests/src/com/android/inputmethod/latin/utils/UserHistoryDictIOUtilsTests.java
index 1944fd3..660e53e 100644
--- a/tests/src/com/android/inputmethod/latin/utils/UserHistoryDictIOUtilsTests.java
+++ b/tests/src/com/android/inputmethod/latin/utils/UserHistoryDictIOUtilsTests.java
@@ -26,6 +26,7 @@
 import com.android.inputmethod.latin.makedict.FormatSpec;
 import com.android.inputmethod.latin.makedict.FusionDictionary;
 import com.android.inputmethod.latin.makedict.FusionDictionary.PtNode;
+import com.android.inputmethod.latin.makedict.UnsupportedFormatException;
 import com.android.inputmethod.latin.makedict.Ver3DictDecoder;
 import com.android.inputmethod.latin.makedict.Ver3DictEncoder;
 import com.android.inputmethod.latin.personalization.UserHistoryDictionaryBigramList;
@@ -142,15 +143,10 @@
         UserHistoryDictIOUtils.writeDictionary(dictEncoder, this, bigramList, FORMAT_OPTIONS);
     }
 
-    private void readDictFromFile(final File file, final OnAddWordListener listener) {
+    private void readDictFromFile(final File file, final OnAddWordListener listener)
+            throws IOException, FileNotFoundException, UnsupportedFormatException {
         final DictDecoder dictDecoder = FormatSpec.getDictDecoder(file, DictDecoder.USE_BYTEARRAY);
-        try {
-            dictDecoder.openDictBuffer();
-        } catch (FileNotFoundException e) {
-            Log.e(TAG, "file not found", e);
-        } catch (IOException e) {
-            Log.e(TAG, "IOException", e);
-        }
+        dictDecoder.openDictBuffer();
         UserHistoryDictIOUtils.readDictionaryBinary(dictDecoder, listener);
     }
 
@@ -169,7 +165,8 @@
         checkWordsInFusionDict(fusionDict, addedWords);
     }
 
-    public void testReadAndWrite() {
+    public void testReadAndWrite() throws IOException, FileNotFoundException,
+            UnsupportedFormatException {
         final Context context = getContext();
 
         File file = null;