diff --git a/ansible_mitogen/connection.py b/ansible_mitogen/connection.py
index 966f86c1..71eb78e0 100644
--- a/ansible_mitogen/connection.py
+++ b/ansible_mitogen/connection.py
@@ -419,6 +419,12 @@ class Connection(ansible.plugins.connection.ConnectionBase):
     #: Only sudo, su, and doas are supported for now.
     become_methods = ['sudo', 'su', 'doas']
 
+    #
+    # Note: any of the attributes below may be :data:`None` if the connection
+    # plugin was constructed directly by a non-cooperative action, such as in
+    # the case of the synchronize module.
+    #
+
     #: Set to 'ansible_python_interpreter' by on_action_run().
     python_path = None
 
@@ -449,6 +455,9 @@ class Connection(ansible.plugins.connection.ConnectionBase):
     #: Set to 'hostvars' by on_action_run()
     host_vars = None
 
+    #: Set by on_action_run()
+    delegate_to_hostname = None
+
     #: Set to '_loader.get_basedir()' by on_action_run(). Used by mitogen_local
     #: to change the working directory to that of the current playbook,
     #: matching vanilla Ansible behaviour.
diff --git a/tests/ansible/integration/action/all.yml b/tests/ansible/integration/action/all.yml
index 22904c23..c5cb80d7 100644
--- a/tests/ansible/integration/action/all.yml
+++ b/tests/ansible/integration/action/all.yml
@@ -3,4 +3,5 @@
 - import_playbook: make_tmp_path.yml
 - import_playbook: remote_expand_user.yml
 - import_playbook: remote_file_exists.yml
+- import_playbook: synchronize.yml
 - import_playbook: transfer_data.yml
diff --git a/tests/ansible/integration/action/synchronize.yml b/tests/ansible/integration/action/synchronize.yml
new file mode 100644
index 00000000..f9a8cb2c
--- /dev/null
+++ b/tests/ansible/integration/action/synchronize.yml
@@ -0,0 +1,28 @@
+# Verify basic operation of the synchronize module.
+
+- name: integration/action/synchronize.yml
+  hosts: test-targets
+  any_errors_fatal: true
+  tasks:
+    - file:
+        path: /tmp/sync-test
+        state: directory
+      connection: local
+
+    - copy:
+        dest: /tmp/sync-test/item
+        content: "item!"
+      connection: local
+
+    - synchronize:
+        dest: /tmp/sync-test
+        src: /tmp/sync-test
+
+    - slurp:
+        src: /tmp/sync-test/item
+      register: out
+
+    - set_fact: outout="{{out.content|b64decode}}"
+
+    - assert:
+        that: outout == "item!"