diff --git a/qobject/json-parser.c b/qobject/json-parser.c
index 5a840dfd860735d3f7a2bea8b91cfb2dbc01e6d9..7a7ae9e8d1a860439c83c079c29a7ca94599d4a5 100644
--- a/qobject/json-parser.c
+++ b/qobject/json-parser.c
@@ -288,6 +288,11 @@ static int parse_pair(JSONParserContext *ctxt, QDict *dict)
         goto out;
     }
 
+    if (qdict_haskey(dict, qstring_get_str(key))) {
+        parse_error(ctxt, token, "duplicate key");
+        goto out;
+    }
+
     qdict_put_obj(dict, qstring_get_str(key), value);
 
     qobject_unref(key);
diff --git a/tests/qemu-iotests/229 b/tests/qemu-iotests/229
index 86602437fff07fc7e7b681da52db08437dcdd7a5..893d098ad23653d13caa5e08d3af5a8c1ad16628 100755
--- a/tests/qemu-iotests/229
+++ b/tests/qemu-iotests/229
@@ -69,7 +69,6 @@ echo
 _send_qemu_cmd $QEMU_HANDLE \
     "{'execute': 'drive-mirror',
                  'arguments': {'device': 'testdisk',
-                               'mode':   'absolute-paths',
                                'format': '$IMGFMT',
                                'target': '$DEST_IMG',
                                'sync':   'full',