diff --git a/ansible_mitogen/target.py b/ansible_mitogen/target.py
index 58b715ce..e891730e 100644
--- a/ansible_mitogen/target.py
+++ b/ansible_mitogen/target.py
@@ -502,7 +502,7 @@ class AsyncRunner(object):
         )
         result = json.loads(filtered)
         result.setdefault('warnings', []).extend(warnings)
-        result['stderr'] = dct['stderr']
+        result['stderr'] = dct['stderr'] or result.get('stderr', '')
         self._update(result)
 
     def _run(self):
diff --git a/docs/changelog.rst b/docs/changelog.rst
index b037ace1..e7ce61c3 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -144,6 +144,9 @@ Fixes
 * `#538 <https://github.com/dw/mitogen/issues/538>`_: the Mitogen source
   distribution includes a requisite ``LICENSE`` file.
 
+* `#540 <https://github.com/dw/mitogen/issues/540>`_: the ``stderr`` stream of
+  async module invocations was previously discarded.
+
 * `748f5f67 <https://github.com/dw/mitogen/commit/748f5f67>`_: the
   ``ansible_ssh_host`` variable is respected when ``mitogen_via=`` is active.
 
diff --git a/tests/ansible/integration/async/result_shell_echo_hi.yml b/tests/ansible/integration/async/result_shell_echo_hi.yml
index c2d2dc42..e1068587 100644
--- a/tests/ansible/integration/async/result_shell_echo_hi.yml
+++ b/tests/ansible/integration/async/result_shell_echo_hi.yml
@@ -5,7 +5,7 @@
   any_errors_fatal: true
   tasks:
 
-  - shell: echo hi
+  - shell: echo hi; echo there >&2
     async: 100
     poll: 0
     register: job
@@ -21,10 +21,10 @@
   - assert:
       that:
         - async_out.changed == True
-        - async_out.cmd == "echo hi"
+        - async_out.cmd == "echo hi; echo there >&2"
         - 'async_out.delta.startswith("0:00:")'
         - async_out.end.startswith("20")
-        - async_out.invocation.module_args._raw_params == "echo hi"
+        - async_out.invocation.module_args._raw_params == "echo hi; echo there >&2"
         - async_out.invocation.module_args._uses_shell == True
         - async_out.invocation.module_args.chdir == None
         - async_out.invocation.module_args.creates == None
@@ -33,7 +33,7 @@
         - async_out.invocation.module_args.warn == True
         - async_out.rc == 0
         - async_out.start.startswith("20")
-        - async_out.stderr == ""
+        - async_out.stderr == "there"
         - async_out.stdout == "hi"
     vars:
       async_out: "{{result.content|b64decode|from_json}}"