diff --git a/src/include/86box/86box.h b/src/include/86box/86box.h
index 10fcd0096..977d3db63 100644
--- a/src/include/86box/86box.h
+++ b/src/include/86box/86box.h
@@ -163,8 +163,8 @@ extern void pclog_ex(const char *fmt, va_list);
 extern void fatal_ex(const char *fmt, va_list);
 #endif
 extern void pclog_toggle_suppr(void);
-extern void pclog(const char *fmt, ...);
-extern void fatal(const char *fmt, ...);
+extern void pclog(const char *fmt, ...) __attribute__ ((format (printf, 1, 2)));
+extern void fatal(const char *fmt, ...) __attribute__ ((format (printf, 1, 2)));
 extern void set_screen_size(int x, int y);
 extern void set_screen_size_monitor(int x, int y, int monitor_index);
 extern void reset_screen_size(void);