diff --git a/Lib/plat-mac/bundlebuilder.py b/Lib/plat-mac/bundlebuilder.py
index 749d851..45642bd 100755
--- a/Lib/plat-mac/bundlebuilder.py
+++ b/Lib/plat-mac/bundlebuilder.py
@@ -127,6 +127,8 @@
 			else:
 				self.creator = "????"
 		plist.CFBundleSignature = self.creator
+		if not hasattr(plist, "CFBundleIdentifier"):
+			plist.CFBundleIdentifier = self.name
 
 	def build(self):
 		"""Build the bundle."""