diff --git a/tools/shared.c b/tools/shared.c
index 7b354ec5..0a110eec 100644
--- a/tools/shared.c
+++ b/tools/shared.c
@@ -75,7 +75,7 @@ log_handler(struct libinput *li,
 }
 
 void
-tools_usage()
+tools_usage(void)
 {
 	printf("Usage: %s [options] [--udev [<seat>]|--device /dev/input/event0]\n"
 	       "--udev <seat>.... Use udev device discovery (default).\n"
diff --git a/tools/shared.h b/tools/shared.h
index c0bb1036..17fdf37a 100644
--- a/tools/shared.h
+++ b/tools/shared.h
@@ -63,6 +63,6 @@ int tools_parse_args(int argc, char **argv, struct tools_context *context);
 struct libinput* tools_open_backend(struct tools_context *context);
 void tools_device_apply_config(struct libinput_device *device,
 			       struct tools_options *options);
-void tools_usage();
+void tools_usage(void);
 
 #endif