diff --git a/DCCEXParser.h b/DCCEXParser.h
index 227e3f0..d9fe0e1 100644
--- a/DCCEXParser.h
+++ b/DCCEXParser.h
@@ -60,6 +60,7 @@ struct DCCEXParser
     static int16_t stashP[MAX_COMMAND_PARAMS];
     static bool stashCallback(Print * stream, int16_t p[MAX_COMMAND_PARAMS], RingStream * ringStream);
     static void callback_W(int16_t result);
+    static void callback_W4(int16_t result);
     static void callback_B(int16_t result);        
     static void callback_R(int16_t result);
     static void callback_Rloco(int16_t result);