diff --git a/apisix/plugins/jwt-auth.lua b/apisix/plugins/jwt-auth.lua
index 26211b98dece..9fdc7a9b5b18 100644
--- a/apisix/plugins/jwt-auth.lua
+++ b/apisix/plugins/jwt-auth.lua
@@ -254,7 +254,8 @@ local function get_real_payload(key, auth_conf, payload)
     }
     if payload then
         local extra_payload = core.json.decode(payload)
-        core.table.merge(real_payload, extra_payload)
+        core.table.merge(extra_payload, real_payload)
+        return extra_payload
     end
     return real_payload
 end
diff --git a/t/plugin/jwt-auth4.t b/t/plugin/jwt-auth4.t
new file mode 100644
index 000000000000..f91b233f4c4f
--- /dev/null
+++ b/t/plugin/jwt-auth4.t
@@ -0,0 +1,122 @@
+#
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You under the Apache License, Version 2.0
+# (the "License"); you may not use this file except in compliance with
+# the License.  You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+BEGIN {
+    $ENV{VAULT_TOKEN} = "root";
+}
+
+use t::APISIX 'no_plan';
+
+repeat_each(1);
+no_long_string();
+no_root_location();
+no_shuffle();
+
+add_block_preprocessor(sub {
+    my ($block) = @_;
+
+    if ((!defined $block->error_log) && (!defined $block->no_error_log)) {
+        $block->set_value("no_error_log", "[error]");
+    }
+
+    if (!defined $block->request) {
+        $block->set_value("request", "GET /t");
+        if (!$block->response_body) {
+            $block->set_value("response_body", "passed\n");
+        }
+    }
+});
+
+run_tests;
+
+__DATA__
+
+=== TEST 1: verify the real_payload's value (key & exp) is not overridden by malicious payload
+--- config
+    location /t {
+        content_by_lua_block {
+            local core = require("apisix.core")
+            local t = require("lib.test_admin").test
+
+            -- prepare consumer
+            local csm_code, csm_body = t('/apisix/admin/consumers',
+                ngx.HTTP_PUT,
+                [[{
+                    "username": "jack",
+                    "plugins": {
+                        "jwt-auth": {
+                            "key": "user-key",
+                            "secret": "my-secret-key"
+                        }
+                    }
+                }]]
+            )
+
+            if csm_code >= 300 then
+                ngx.status = csm_code
+                ngx.say(csm_body)
+                return
+            end
+
+            -- prepare sign api
+            local rot_code, rot_body = t('/apisix/admin/routes/2',
+                ngx.HTTP_PUT,
+                [[{
+                    "plugins": {
+                        "public-api": {}
+                    },
+                    "uri": "/apisix/plugin/jwt/sign"
+                }]]
+            )
+
+            if rot_code >= 300 then
+                ngx.status = rot_code
+                ngx.say(rot_body)
+                return
+            end
+
+            -- generate jws
+            local code, err, sign = t('/apisix/plugin/jwt/sign?key=user-key&payload={"key":"letmein","exp":1234567890}',
+                ngx.HTTP_GET
+            )
+
+            if code > 200 then
+                ngx.status = code
+                ngx.say(err)
+                return
+            end
+
+            -- get payload section from jws
+            local payload = string.match(sign,"^.+%.(.+)%..+$")
+
+            if not payload then
+                ngx.say("sign-failed")
+                return
+            end
+
+            -- check payload value
+            local res = core.json.decode(ngx.decode_base64(payload))
+
+            if res.key == 'user-key' and res.exp ~= 1234567890 then
+               ngx.say("safe-jws")
+               return
+            end
+
+            ngx.say("fake-jws")
+        }
+    }
+--- response_body
+safe-jws