diff --git a/src/core/pbuf.c b/src/core/pbuf.c
index e2ae0a11..f1718257 100644
--- a/src/core/pbuf.c
+++ b/src/core/pbuf.c
@@ -655,7 +655,7 @@ pbuf_cat(struct pbuf *h, struct pbuf *t)
 
   LWIP_ASSERT("h != NULL", h != NULL);
   LWIP_ASSERT("t != NULL", t != NULL);
-  if ((h = NULL) || (t == NULL)) return;
+  if ((h == NULL) || (t == NULL)) return;
 
   /* proceed to last pbuf of chain */
   for (p = h; p->next != NULL; p = p->next) {