diff --git a/tools/dicttool/src/com/android/inputmethod/latin/dicttool/DictionaryMaker.java b/tools/dicttool/src/com/android/inputmethod/latin/dicttool/DictionaryMaker.java
index 561db7363..cc890f60c 100644
--- a/tools/dicttool/src/com/android/inputmethod/latin/dicttool/DictionaryMaker.java
+++ b/tools/dicttool/src/com/android/inputmethod/latin/dicttool/DictionaryMaker.java
@@ -172,12 +172,15 @@ public class DictionaryMaker {
                         String filename = args.get(0);
                         args.remove(0);
                         if (OPTION_INPUT_SOURCE.equals(arg)) {
-                            if (BinaryDictInputOutput.isBinaryDictionary(filename)) {
-                                inputBinary = filename;
+                            if (XmlDictInputOutput.isXmlUnigramDictionary(filename)) {
+                                inputUnigramXml = filename;
                             } else if (CombinedInputOutput.isCombinedDictionary(filename)) {
                                 inputCombined = filename;
+                            } else if (BinaryDictInputOutput.isBinaryDictionary(filename)) {
+                                inputBinary = filename;
                             } else {
-                                inputUnigramXml = filename;
+                                throw new IllegalArgumentException(
+                                        "Unknown format for file " + filename);
                             }
                         } else if (OPTION_INPUT_SHORTCUT_XML.equals(arg)) {
                             inputShortcutXml = filename;
diff --git a/tools/dicttool/src/com/android/inputmethod/latin/dicttool/XmlDictInputOutput.java b/tools/dicttool/src/com/android/inputmethod/latin/dicttool/XmlDictInputOutput.java
index 252c3d655..d8d94a13c 100644
--- a/tools/dicttool/src/com/android/inputmethod/latin/dicttool/XmlDictInputOutput.java
+++ b/tools/dicttool/src/com/android/inputmethod/latin/dicttool/XmlDictInputOutput.java
@@ -22,6 +22,10 @@ import com.android.inputmethod.latin.makedict.FusionDictionary.Node;
 import com.android.inputmethod.latin.makedict.FusionDictionary.WeightedString;
 import com.android.inputmethod.latin.makedict.Word;
 
+import java.io.BufferedReader;
+import java.io.File;
+import java.io.FileNotFoundException;
+import java.io.FileReader;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.Writer;
@@ -263,6 +267,35 @@ public class XmlDictInputOutput {
         }
     }
 
+    /**
+     * Basic test to find out whether the file is in the unigram XML format or not.
+     *
+     * Concretely this only tests the header line.
+     *
+     * @param filename The name of the file to test.
+     * @return true if the file is in the unigram XML format, false otherwise
+     */
+    public static boolean isXmlUnigramDictionary(final String filename) {
+        BufferedReader reader = null;
+        try {
+            reader = new BufferedReader(new FileReader(new File(filename)));
+            final String firstLine = reader.readLine();
+            return firstLine.matches("^\\s*<wordlist .*>\\s*$");
+        } catch (FileNotFoundException e) {
+            return false;
+        } catch (IOException e) {
+            return false;
+        } finally {
+            if (reader != null) {
+                try {
+                    reader.close();
+                } catch (IOException e) {
+                    // do nothing
+                }
+            }
+        }
+    }
+
     /**
      * Reads a dictionary from an XML file.
      *