diff --git a/src/libkore.c b/src/libkore.c
index 6430d4e..d23b01d 100644
--- a/src/libkore.c
+++ b/src/libkore.c
@@ -122,7 +122,7 @@ int coroutine_iter_next(struct co_obj *obj){
 		const char *data = luaL_checklstring(L,-1,&size);
 		struct netbuf *nb;
 		struct kore_buf *kb = kore_buf_alloc(4096);
-		kore_buf_appendf(kb,"%x\r\n",size);
+		kore_buf_appendf(kb,"%lu\r\n",size);
 		kore_buf_append(kb,data,size);
 		kore_buf_appendf(kb,"\r\n");
 		//size_t ssize;