diff --git a/sim_defs.h b/sim_defs.h
index 12bf64af..558573ea 100644
--- a/sim_defs.h
+++ b/sim_defs.h
@@ -277,7 +277,7 @@ typedef uint32          t_addr;
 
 /* String match - at least one character required */
 
-#define MATCH_CMD(ptr,cmd) ((!*(ptr)) || strncmp ((ptr), (cmd), strlen (ptr)))
+#define MATCH_CMD(ptr,cmd) ((!(ptr)) || (!*(ptr)) || strncmp ((ptr), (cmd), strlen (ptr)))
 
 /* End of Linked List/Queue value                           */
 /* Chosen for 2 reasons:                                    */