diff --git a/src/server/management/routing-profile-routes.ts b/src/server/management/routing-profile-routes.ts
index 36687c01b3..79a1cf0115 100644
--- a/src/server/management/routing-profile-routes.ts
+++ b/src/server/management/routing-profile-routes.ts
@@ -175,10 +175,10 @@ function modelMapMigrationCollision(
   const map = config.claudeCode?.modelMap;
   if (!map) return null;
   if (oldPublicModel === newPublicModel) return null;
+  if (!Object.hasOwn(map, oldPublicModel)) return null;
   const oldTarget = map[oldPublicModel];
-  if (oldTarget === undefined) return null;
+  if (!Object.hasOwn(map, newPublicModel)) return null;
   const newTarget = map[newPublicModel];
-  if (newTarget === undefined) return null;
   if (oldTarget === newTarget) return null;
   return `modelMap already maps \"${newPublicModel}\" to \"${newTarget}\"; renaming \"${oldPublicModel}\" (→ \"${newTarget}\") would drop one mapping. Resolve the conflict and retry.`;
 }
diff --git a/tests/routing-profile-management-editor.test.ts b/tests/routing-profile-management-editor.test.ts
index 08fc82aa27..859148b6ca 100644
--- a/tests/routing-profile-management-editor.test.ts
+++ b/tests/routing-profile-management-editor.test.ts
@@ -453,6 +453,38 @@ describe("routing profile management editor API", () => {
     expect(saves).toBe(0);
   });
 
+  test("PUT update ignores inherited modelMap properties when checking alias collisions", async () => {
+    const config = baseConfig();
+    config.claudeCode = {
+      enabled: false,
+      modelMap: { "ocx/fast": "a/m1" },
+    };
+    let saves = 0;
+    const req = new ManagementRequest("http://localhost/api/routing-profiles", {
+      method: "PUT",
+      headers: { "content-type": "application/json" },
+      body: JSON.stringify({
+        id: "fast",
+        mode: "update",
+        profile: {
+          alias: "constructor",
+          candidates: [{ provider: "a", model: "m1" }],
+        },
+      }),
+    });
+    const response = await handleManagementAPI(
+      req,
+      new URL(req.url),
+      config,
+      deps(() => { saves += 1; }),
+    );
+
+    expect(response?.status).toBe(200);
+    expect(config.routingProfiles?.fast).toMatchObject({ alias: "constructor" });
+    expect(config.claudeCode?.modelMap).toEqual({ constructor: "a/m1" });
+    expect(saves).toBe(1);
+  });
+
   test("DELETE removes a profile, persists, and refreshes the catalog", async () => {
     const config = baseConfig();
     let saves = 0;