diff --git a/test/common/index.js b/test/common/index.js
index 7489b8faef088a..81e76be0f31b1a 100644
--- a/test/common/index.js
+++ b/test/common/index.js
@@ -40,7 +40,16 @@ const noop = () => {};
 // gets tools to ignore it by default or by simple rules, especially eslint.
 let tmpDirName = '.tmp';
 
-exports.PORT = +process.env.NODE_COMMON_PORT || 12346;
+Object.defineProperty(exports, 'PORT', {
+  get: () => {
+    if (+process.env.TEST_PARALLEL) {
+      throw new Error('common.PORT cannot be used in a parallelized test');
+    }
+    return +process.env.NODE_COMMON_PORT || 12346;
+  },
+  enumerable: true
+});
+
 
 exports.isWindows = process.platform === 'win32';
 exports.isWOW64 = exports.isWindows &&
diff --git a/tools/test.py b/tools/test.py
index ccc25f2a883c15..230774b25619da 100755
--- a/tools/test.py
+++ b/tools/test.py
@@ -532,7 +532,8 @@ def Run(self):
 
     try:
       result = self.RunCommand(self.GetCommand(), {
-        "TEST_THREAD_ID": "%d" % self.thread_id
+        "TEST_THREAD_ID": "%d" % self.thread_id,
+        "TEST_PARALLEL" : "%d" % self.parallel
       })
     finally:
       # Tests can leave the tty in non-blocking mode. If the test runner