diff --git a/glcpp/glcpp-parse.y b/glcpp/glcpp-parse.y
index 807cf595090..ede2bb88fd1 100644
--- a/glcpp/glcpp-parse.y
+++ b/glcpp/glcpp-parse.y
@@ -1356,7 +1356,7 @@ _glcpp_parser_expand_token_list (glcpp_parser_t *parser,
 				else
 					list->head = last->next;
 				if (last == list->tail)
-					list->tail == NULL;
+					list->tail = NULL;
 			}
 		} else {
 			node_prev = node;