diff --git a/lualib-src/lua-bson.c b/lualib-src/lua-bson.c
index 077e538e..ade3cc4e 100644
--- a/lualib-src/lua-bson.c
+++ b/lualib-src/lua-bson.c
@@ -532,6 +532,9 @@ unpack_dict(lua_State *L, struct bson_reader *br, bool array) {
 			break;
 		case BSON_STRING: {
 			int sz = read_int32(L, &t);
+			if (sz == 0) {
+				luaL_error(L, "Invalid bson string , length = 0");
+			}
 			lua_pushlstring(L, read_bytes(L, &t, sz), sz-1);
 			break;
 		}
@@ -804,6 +807,9 @@ lreplace(lua_State *L) {
 		write_int64(&b, i);
 		break;
 	}
+	default:
+		luaL_error(L, "Can't replace type %d", type);
+		break;
 	}
 	return 0;
 }