diff --git a/litellm/proxy/credential_endpoints/endpoints.py b/litellm/proxy/credential_endpoints/endpoints.py
index 09d9fcedb3b..8df22f458cf 100644
--- a/litellm/proxy/credential_endpoints/endpoints.py
+++ b/litellm/proxy/credential_endpoints/endpoints.py
@@ -181,8 +181,9 @@ def _not_found_unless_config_defined(credential_name: str, not_found_detail: str
     return ProxyException(
         message=f"Credential '{credential_name}' is defined in config and cannot be edited from the API or UI.",
         type=ProxyErrorTypes.validation_error.value,
-        code=status.HTTP_400_BAD_REQUEST,
+        code=status.HTTP_405_METHOD_NOT_ALLOWED,
         param="credential_name",
+        headers={"Allow": "GET"},
     )
 
 
diff --git a/tests/unit/proxy/credential_endpoints/test_endpoints.py b/tests/unit/proxy/credential_endpoints/test_endpoints.py
index 9c94b47b8f4..83d6167256a 100644
--- a/tests/unit/proxy/credential_endpoints/test_endpoints.py
+++ b/tests/unit/proxy/credential_endpoints/test_endpoints.py
@@ -999,7 +999,8 @@ class TestNonAdminCannotTouchAStoredWifCredential:
         with _repository_holding(None) as repository:
             response = _delete_credential("config-wif", auth=_as_admin)
 
-        assert response.status_code == 400, response.text
+        assert response.status_code == 405, response.text
+        assert response.headers["allow"] == "GET"
         assert "defined in config" in response.json()["error"]["message"]
         repository.delete_by_name.assert_awaited_once_with("config-wif")
         assert litellm.credential_list == [config_credential]
@@ -1198,7 +1199,8 @@ def test_delete_credential_leaves_a_credential_that_only_exists_in_memory_in_pla
 
     response = _delete_credential("from-config-yaml")
 
-    assert response.status_code == 400, response.text
+    assert response.status_code == 405, response.text
+    assert response.headers["allow"] == "GET"
     assert "defined in config" in response.json()["error"]["message"]
     assert [credential.credential_name for credential in litellm.credential_list] == ["from-config-yaml"]
 
@@ -1526,7 +1528,8 @@ class TestCredentialDisplayName:
         with _repository_holding(None) as repository:
             response = _patch_credential("openai-prod", {"display_name": "Prod", "credential_info": {}})
 
-        assert response.status_code == 400, response.text
+        assert response.status_code == 405, response.text
+        assert response.headers["allow"] == "GET"
         assert "defined in config" in response.json()["error"]["message"]
         repository.update_by_name.assert_not_awaited()
         assert litellm.credential_list == [config_credential]