diff --git a/__tests__/util.test.ts b/__tests__/util.test.ts
index d60c051c..db5cd10a 100644
--- a/__tests__/util.test.ts
+++ b/__tests__/util.test.ts
@@ -95,7 +95,7 @@ describe('isGhes', () => {
   });  
 
   it('returns false when the GITHUB_SERVER_URL environment variable is not defined', async () => {
-    process.env['GITHUB_SERVER_URL'] = undefined;
+    delete process.env['GITHUB_SERVER_URL'];
     expect(isGhes()).toBeFalsy();
   });
 
@@ -119,4 +119,3 @@ describe('isGhes', () => {
     expect(isGhes()).toBeTruthy();
   });
 });
-