diff --git a/src/debug.h b/src/debug.h
--- a/src/debug.h
+++ b/src/debug.h
@@ -29,7 +29,7 @@
 #ifdef NO_DEBUG_MESSAGES
 	#define DEBUG(name, level, ...) { }
 #else /* NO_DEBUG_MESSAGES */
-	#define DEBUG(name, level, ...) if (level == 0 || _debug_ ## name ## _level >= level) debug(#name, __VA_ARGS__)
+	#define DEBUG(name, level, ...) if ((level) == 0 || _debug_ ## name ## _level >= (level)) debug(#name, __VA_ARGS__)
 
 	extern int _debug_ai_level;
 	extern int _debug_driver_level;