diff --git a/eslint.config.mjs b/eslint.config.mjs
index dec0b60327..2ed8169174 100644
--- a/eslint.config.mjs
+++ b/eslint.config.mjs
@@ -117,6 +117,14 @@ const config = createConfig([
       },
     },
     rules: {
+      // These rules have been customized from their defaults.
+      '@typescript-eslint/switch-exhaustiveness-check': [
+        'error',
+        {
+          considerDefaultExhaustiveForUnions: true,
+        },
+      ],
+
       // This rule does not detect multiple imports of the same file where types
       // are being imported in one case and runtime values are being imported in
       // another
@@ -151,7 +159,6 @@ const config = createConfig([
       '@typescript-eslint/only-throw-error': 'warn',
       '@typescript-eslint/prefer-promise-reject-errors': 'warn',
       '@typescript-eslint/prefer-readonly': 'warn',
-      '@typescript-eslint/switch-exhaustiveness-check': 'warn',
       'import-x/namespace': 'warn',
       'import-x/no-named-as-default': 'warn',
       'import-x/order': 'warn',