diff --git a/CHANGES b/CHANGES
index 62e1f60ee2f..c01529a7113 100644
--- a/CHANGES
+++ b/CHANGES
@@ -27,6 +27,7 @@ Bugs fixed
   with Japanese engines
 * #9354: C, remove special macro names from the keyword list.
   See also :confval:`c_extra_keywords`.
+* #9322: KeyError is raised on PropagateDescDomain transform
 
 Testing
 --------
diff --git a/sphinx/transforms/post_transforms/__init__.py b/sphinx/transforms/post_transforms/__init__.py
index dde06fae1be..7f4b3e3a691 100644
--- a/sphinx/transforms/post_transforms/__init__.py
+++ b/sphinx/transforms/post_transforms/__init__.py
@@ -249,7 +249,8 @@ class PropagateDescDomain(SphinxPostTransform):
 
     def run(self, **kwargs: Any) -> None:
         for node in self.document.traverse(addnodes.desc_signature):
-            node['classes'].append(node.parent['domain'])
+            if node.parent.get('domain'):
+                node['classes'].append(node.parent['domain'])
 
 
 def setup(app: Sphinx) -> Dict[str, Any]: