diff --git a/java/src/com/android/inputmethod/latin/makedict/Ver4DictDecoder.java b/java/src/com/android/inputmethod/latin/makedict/Ver4DictDecoder.java
index 23aa05d..88fff38 100644
--- a/java/src/com/android/inputmethod/latin/makedict/Ver4DictDecoder.java
+++ b/java/src/com/android/inputmethod/latin/makedict/Ver4DictDecoder.java
@@ -53,6 +53,10 @@
 
     @Override
     public DictionaryHeader readHeader() throws IOException, UnsupportedFormatException {
+        final DictionaryHeader header = mBinaryDictionary.getHeader();
+        if (header == null) {
+            throw new IOException("Cannot read the dictionary header.");
+        }
         return mBinaryDictionary.getHeader();
     }