diff --git a/scp.h b/scp.h
index 52cf2b9f..4a50cffc 100644
--- a/scp.h
+++ b/scp.h
@@ -131,7 +131,7 @@ void sim_debug (uint32 dbits, DEVICE* dptr, const char* fmt, ...);
 #else
 void _sim_debug (uint32 dbits, DEVICE* dptr, const char* fmt, ...);
 extern FILE *sim_deb;                                   /* debug file */
-#define sim_debug(dbits, dptr, ...) if (sim_deb && ((dptr)->dctrl & dbits)) _sim_debug (dbits, dptr, __VA_ARGS__)
+#define sim_debug(dbits, dptr, ...) if (sim_deb && ((dptr)->dctrl & dbits)) _sim_debug (dbits, dptr, __VA_ARGS__); else 0
 #endif
 void fprint_stopped_gen (FILE *st, t_stat v, REG *pc, DEVICE *dptr);