diff --git a/ansible_mitogen/helpers.py b/ansible_mitogen/helpers.py
index f561c877..270f3244 100644
--- a/ansible_mitogen/helpers.py
+++ b/ansible_mitogen/helpers.py
@@ -94,7 +94,7 @@ def run_module(kwargs):
     runner_name = kwargs.pop('runner_name')
     klass = getattr(ansible_mitogen.runner, runner_name)
     impl = klass(**kwargs)
-    return json.dumps(impl.run())
+    return impl.run()
 
 
 def _async_main(job_id, runner_name, kwargs):
diff --git a/ansible_mitogen/mixins.py b/ansible_mitogen/mixins.py
index 2ed7139a..831d77eb 100644
--- a/ansible_mitogen/mixins.py
+++ b/ansible_mitogen/mixins.py
@@ -315,18 +315,22 @@ class ActionModuleMixin(ansible.plugins.action.ActionBase):
             )
         )
 
-    def _postprocess_response(self, js):
+    def _postprocess_response(self, result):
         """
         Apply fixups mimicking ActionBase._execute_module(); this is copied
         verbatim from action/__init__.py, the guts of _parse_returned_data are
         garbage and should be removed or reimplemented once tests exist.
+
+        :param dict result:
+            Dictionary with format::
+
+                {
+                    "rc": int,
+                    "stdout": "stdout data",
+                    "stderr": "stderr data"
+                }
         """
-        data = self._parse_returned_data({
-            'rc': 0,
-            'stdout': js,
-            'stdout_lines': [js],
-            'stderr': ''
-        })
+        data = self._parse_returned_data(result)
 
         # Cutpasted from the base implementation.
         if 'stdout' in data and 'stdout_lines' not in data:
diff --git a/ansible_mitogen/runner.py b/ansible_mitogen/runner.py
index 84d06297..ad94ef7c 100644
--- a/ansible_mitogen/runner.py
+++ b/ansible_mitogen/runner.py
@@ -87,6 +87,16 @@ class Runner(object):
         self._env.revert()
 
     def _run(self):
+        """
+        The _run() method is expected to return a dictionary in the form of
+        ActionBase._low_level_execute_command() output, i.e. having::
+
+            {
+                "rc": int,
+                "stdout": "stdout data",
+                "stderr": "stderr data"
+            }
+        """
         raise NotImplementedError()
 
     def run(self):
@@ -224,11 +234,16 @@ class NativeRunner(Runner):
             # to invoke main explicitly.
             mod.main()
         except NativeModuleExit, e:
-            return e.dct
+            return {
+                'rc': 0,
+                'stdout': json.dumps(e.dct),
+                'stderr': '',
+            }
 
         return {
-            'failed': True,
-            'msg': 'ansible_mitogen: module did not exit normally.'
+            'rc': 1,
+            'stdout': '',
+            'stderr': 'ansible_mitogen: module did not exit normally.',
         }
 
 
@@ -299,8 +314,9 @@ class BinaryRunner(Runner):
             )
         except Exception, e:
             return {
-                'failed': True,
-                'msg': '%s: %s' % (type(e), e),
+                'rc': 1,
+                'stdout': '',
+                'stderr': '%s: %s' % (type(e), e),
             }
 
         return {