diff --git a/ui-diff.h b/ui-diff.h
index 04f9029..382e8c5 100644
--- a/ui-diff.h
+++ b/ui-diff.h
@@ -1,7 +1,7 @@
 #ifndef UI_DIFF_H
 #define UI_DIFF_H
 
-extern void cgit_print_diff_ctrls();
+extern void cgit_print_diff_ctrls(void);
 
 extern void cgit_print_diff(const char *new_hex, const char *old_hex,
 			    const char *prefix, int show_ctrls, int raw);