diff --git a/sql/debug_sync.cc b/sql/debug_sync.cc
index 5847394ae51..108f9686def 100644
--- a/sql/debug_sync.cc
+++ b/sql/debug_sync.cc
@@ -1979,6 +1979,11 @@ bool debug_sync_set_action(THD *thd, const char *action_str, size_t len) {
   assert(thd);
   assert(action_str);
 
+  // A zero value keeps the facility disabled.
+  if (!opt_debug_sync_timeout) {
+    return false;
+  }
+
   value = strmake_root(thd->mem_root, action_str, len);
   rc = debug_sync_eval_action(thd, value);
   return rc;