diff --git a/test/unit/adapters/http.js b/test/unit/adapters/http.js
index 6fa99bd..ba59558 100644
--- a/test/unit/adapters/http.js
+++ b/test/unit/adapters/http.js
@@ -15,7 +15,7 @@ module.exports = {
     }
 
     if (process.env.http_proxy) {
-      process.env.http_proxy = null;
+      delete process.env.http_proxy;
     }
 
     callback();