diff --git a/tools/crm_mon.c b/tools/crm_mon.c
index 0981634..1eca1b7 100644
--- a/tools/crm_mon.c
+++ b/tools/crm_mon.c
@@ -1226,7 +1226,7 @@ handle_connection_failures(int rc)
 }
 
 static void
-one_shot()
+one_shot(void)
 {
     int rc;