diff --git a/src/LitJson/JsonMapper.cs b/src/LitJson/JsonMapper.cs
index 38d68a7..a674191 100644
--- a/src/LitJson/JsonMapper.cs
+++ b/src/LitJson/JsonMapper.cs
@@ -755,7 +755,7 @@ private static void WriteValue (object obj, JsonWriter writer,
             if (obj is IDictionary) {
                 writer.WriteObjectStart ();
                 foreach (DictionaryEntry entry in (IDictionary) obj) {
-                    writer.WritePropertyName ((string) entry.Key);
+                    writer.WritePropertyName (entry.Key.ToString());
                     WriteValue (entry.Value, writer, writer_is_private,
                                 depth + 1);
                 }
diff --git a/test/JsonMapperTest.cs b/test/JsonMapperTest.cs
index 8a3421f..64e9dcb 100644
--- a/test/JsonMapperTest.cs
+++ b/test/JsonMapperTest.cs
@@ -283,12 +283,12 @@ public void ExportDictionaryTest ()
             hash.Add ("product", "ACME rocket skates");
             hash.Add ("quantity", 5);
             hash.Add ("price", 45.95);
+            hash.Add (1L, "Cast long to string");
 
             string expected = "{\"product\":\"ACME rocket skates\"," +
-                "\"quantity\":5,\"price\":45.95}";
+                "\"quantity\":5,\"price\":45.95,\"1\":\"Cast long to string\"}";
 
             string json = JsonMapper.ToJson (hash);
-
             Assert.AreEqual (expected, json);
         }