Index: Lib/plat-mac/buildtools.py
===================================================================
--- Lib/plat-mac/buildtools.py	(revision 57912)
+++ Lib/plat-mac/buildtools.py	(working copy)
@@ -17,7 +17,8 @@
 warnings.warn("the buildtools module is deprecated", DeprecationWarning, 2)
 
 
-BuildError = "BuildError"
+class BuildError(BaseException):
+    pass
 
 # .pyc file (and 'PYC ' resource magic number)
 MAGIC = imp.get_magic()
Index: Lib/plat-mac/bundlebuilder.py
===================================================================
--- Lib/plat-mac/bundlebuilder.py	(revision 57912)
+++ Lib/plat-mac/bundlebuilder.py	(working copy)
@@ -180,8 +180,9 @@
         assert len(self.type) == len(self.creator) == 4, \
                 "type and creator must be 4-byte strings."
         pkginfo = pathjoin(contents, "PkgInfo")
+        data = bytes(self.type + self.creator, encoding='ascii')
         f = open(pkginfo, "wb")
-        f.write(self.type + self.creator)
+        f.write(data)
         f.close()
         #
         # Write Contents/Info.plist