diff --git a/src/agents/schema/clean-for-gemini.ts b/src/agents/schema/clean-for-gemini.ts
index d87bcdcbbc8..5208e790abd 100644
--- a/src/agents/schema/clean-for-gemini.ts
+++ b/src/agents/schema/clean-for-gemini.ts
@@ -198,11 +198,13 @@ function cleanSchemaForGeminiWithDefs(
       const result: Record<string, unknown> = {
         ...(cleaned as Record<string, unknown>),
       };
-      for (const key of ["description", "title", "default"]) {
-        if (key in obj && obj[key] !== undefined) {
-          result[key] = obj[key];
-        }
-      }
+      // Preserve all sibling properties except "$ref"
+for (const [key, value] of Object.entries(obj)) {
+  if (key !== "$ref" && value !== undefined) {
+    result[key] = value;
+  }
+}
+
       return result;
     }