diff --git a/include/openbsc/debug.h b/include/openbsc/debug.h
index 02ae699..b95b1a7 100644
--- a/include/openbsc/debug.h
+++ b/include/openbsc/debug.h
@@ -17,6 +17,6 @@
 #define DEBUGP(xss, fmt, args...) 
 #endif
 
-void debugp(int subsys, char *file, int line, const char *format, ...);
+void debugp(unsigned int subsys, char *file, int line, const char *format, ...);
 
 #endif /* _DEBUG_H */