diff --git a/ext/spl/spl_dllist.c b/ext/spl/spl_dllist.c
index c576104139315..c6a022e8b7f7f 100644
--- a/ext/spl/spl_dllist.c
+++ b/ext/spl/spl_dllist.c
@@ -1257,6 +1257,7 @@ PHP_METHOD(SplDoublyLinkedList, add)
 
 		/* Get the element we want to insert before */
 		element = spl_ptr_llist_offset(intern->llist, index, intern->flags & SPL_DLLIST_IT_LIFO);
+		ZEND_ASSERT(element != NULL);
 
 		ZVAL_COPY_VALUE(&elem->data, value);
 		SPL_LLIST_RC(elem) = 1;