diff --git a/lualib-src/lua-mongo.c b/lualib-src/lua-mongo.c
index a8ca0b0c..4ceffa06 100644
--- a/lualib-src/lua-mongo.c
+++ b/lualib-src/lua-mongo.c
@@ -246,6 +246,9 @@ op_reply(lua_State *L) {
 			lua_rawseti(L, 2, i);
 
 			int32_t doc_len = get_length((document)doc);
+			if (doc_len <= 0) {
+				return luaL_error(L, "Invalid result bson document");
+			}
 
 			doc += doc_len;
 			sz -= doc_len;