diff --git a/src/core/pbuf.c b/src/core/pbuf.c
index 470a6230..9f35ec6a 100644
--- a/src/core/pbuf.c
+++ b/src/core/pbuf.c
@@ -743,17 +743,17 @@ pbuf_free(struct pbuf *p)
   /* de-allocate all consecutive pbufs from the head of the chain that
    * obtain a zero reference count after decrementing*/
   while (p != NULL) {
-    LWIP_PBUF_REF_T ref;
+    u16_t ref;
     SYS_ARCH_DECL_PROTECT(old_level);
     /* Since decrementing ref cannot be guaranteed to be a single machine operation
      * we must protect it. We put the new ref into a local variable to prevent
      * further protection. */
     SYS_ARCH_PROTECT(old_level);
+    /* all pbufs in a chain are referenced at least once */
+    LWIP_ASSERT("pbuf_free: p->ref > 0", p->ref > 0);
     /* decrease reference count (number of pointers to pbuf) */
     ref = --(p->ref);
     SYS_ARCH_UNPROTECT(old_level);
-    /* Check for refcount underflow */
-    LWIP_ASSERT("pbuf_free: p->ref >= 0", ref >= 0);
     /* this pbuf is no longer referenced to? */
     if (ref == 0) {
       /* remember next pbuf in chain for next iteration */