diff --git a/lib/galaxy/schema/workflows.py b/lib/galaxy/schema/workflows.py
index 851ac1a24359..78784d792053 100644
--- a/lib/galaxy/schema/workflows.py
+++ b/lib/galaxy/schema/workflows.py
@@ -833,7 +833,7 @@ class WorkflowDictPreviewSummary(WorkflowDictExtendedBaseModel):
 
 
 class WorkflowDictEditorSummary(WorkflowDictExtendedBaseModel):
-    upgrade_messages: Dict[int, Union[str, Dict[str, str]]] = Field(
+    upgrade_messages: Dict[int, Union[str, Dict[str, Union[str, Dict[str, str]]]]] = Field(
         ...,
         title="Upgrade Messages",
         description="Upgrade messages for each step in the workflow.",