diff --git a/xkbcat.c b/xkbcat.c
index 5e28cc2..e6e73bf 100644
--- a/xkbcat.c
+++ b/xkbcat.c
@@ -11,7 +11,7 @@
 const char * DEFAULT_DISPLAY    = ":0";
 const bool   DEFAULT_PRINT_UP   = false;
 
-int printUsage() {
+int printUsage(void) {
     printf("\
 USAGE: xkbcat [-display <display>] [-up]\n\
     display  target X display                   (default %s)\n\