diff --git a/src/core/pbuf.c b/src/core/pbuf.c
index 4ca95b9a..059f83a5 100644
--- a/src/core/pbuf.c
+++ b/src/core/pbuf.c
@@ -822,6 +822,7 @@ pbuf_ref(struct pbuf *p)
   /* pbuf given? */
   if (p != NULL) {
     SYS_ARCH_INC(p->ref, 1);
+    LWIP_ASSERT("pbuf ref overflow", p->ref > 0);
   }
 }