diff --git a/mandayejs/mandaye/utils.py b/mandayejs/mandaye/utils.py
index 73c128e..9d51f7a 100644
--- a/mandayejs/mandaye/utils.py
+++ b/mandayejs/mandaye/utils.py
@@ -37,7 +37,8 @@ def run(send_end, data, script):
         os.path.join(settings.BASE_DIR, 'mandayejs', script)],
         close_fds=True,
         stdin=subprocess.PIPE,
-        stdout=subprocess.PIPE
+        stdout=subprocess.PIPE,
+        stderr=subprocess.PIPE
     )
     stdout, stderr = phantom.communicate(json.dumps(data))
 
@@ -49,7 +50,7 @@ def run(send_end, data, script):
         result = json.loads(stdout)
     except (ValueError,):
         result = {"result": "json_error"}
-        logger.error("invalid json: %s" % stdout)
+        logger.error("invalid json: %s (stderr: %s)", stdout, stderr)
 
     if result.get('stderr'):
         logger.warning(result['stderr'])
diff --git a/tests/test_mandayejs.py b/tests/test_mandayejs.py
index a7c0671..ef5f98c 100644
--- a/tests/test_mandayejs.py
+++ b/tests/test_mandayejs.py
@@ -100,7 +100,7 @@ def test_command_migrate_users(mocked_idps, command):
 @mock.patch('mandayejs.mandaye.utils.subprocess.Popen')
 @mock.patch('mandayejs.applications.Test.SITE_LOCATORS', MOCKED_SITE_LOCATORS)
 def test_phantom_invalid_json(mocked_popen, caplog, user_john):
-    expected_output = ('This is not a valid JSON', None)
+    expected_output = ('This is not a valid JSON', 'msg on stderr')
     mocked_popen.return_value = MockedPopen(expected_output=expected_output)
 
     UserCredentials.objects.create(user=user_john,
@@ -119,7 +119,7 @@ def test_phantom_invalid_json(mocked_popen, caplog, user_john):
 
     for record in caplog.records:
         if record.levelname == 'ERROR':
-            assert record.message == 'invalid json: This is not a valid JSON'
+            assert record.message == 'invalid json: This is not a valid JSON (stderr: msg on stderr)'
 
 
 @mock.patch('mandayejs.mandaye.utils.subprocess.Popen')