diff --git a/server/mpm/event/event.c b/server/mpm/event/event.c
index df320b5667..371eb6620d 100644
--- a/server/mpm/event/event.c
+++ b/server/mpm/event/event.c
@@ -1155,6 +1155,7 @@ static void * APR_THREAD_FUNC listener_thread(apr_thread_t * thd, void *dummy)
                                  ap_server_conf,
                                  "event_loop: unexpected state %d",
                                  cs->state);
+                    AP_DEBUG_ASSERT(0);
                 }
 
                 apr_thread_mutex_lock(timeout_mutex);
diff --git a/server/mpm/event/fdqueue.c b/server/mpm/event/fdqueue.c
index 7d7d4d019e..10015b7d39 100644
--- a/server/mpm/event/fdqueue.c
+++ b/server/mpm/event/fdqueue.c
@@ -165,6 +165,7 @@ apr_status_t ap_queue_info_wait_for_idler(fd_queue_info_t * queue_info)
                                       queue_info->idlers_mutex);
             if (rv != APR_SUCCESS) {
                 apr_status_t rv2;
+                AP_DEBUG_ASSERT(0);
                 rv2 = apr_thread_mutex_unlock(queue_info->idlers_mutex);
                 if (rv2 != APR_SUCCESS) {
                     return rv2;