diff --git a/src/core/timers.c b/src/core/timers.c
index d5f17d4a..97628c7d 100644
--- a/src/core/timers.c
+++ b/src/core/timers.c
@@ -260,7 +260,7 @@ sys_timeout(u32_t msecs, sys_timeout_handler h, void *arg)
 
   timeout = memp_malloc(MEMP_SYS_TIMEOUT);
   if (timeout == NULL) {
-    LWIP_ASSERT("sys_timeout: timeout != NULL", timeout != NULL);
+    LWIP_ASSERT("sys_timeout: timeout != NULL, pool MEMP_SYS_TIMEOUT is empty", timeout != NULL);
     return;
   }
   timeout->next = NULL;