diff --git a/src/backends/exec.c b/src/backends/exec.c
index 1f221ef..b16a97a 100644
--- a/src/backends/exec.c
+++ b/src/backends/exec.c
@@ -268,6 +268,7 @@ check(cfg_t *cfg, const char *ip) {
 bool
 ping(cfg_t *cfg) {
   assert(cfg != NULL);
+  (void)(cfg); /* suppress warning about unused variable */
   return true;
 }