diff --git a/Mac/scripts/fixgusidir.py b/Mac/scripts/fixgusidir.py
new file mode 100644
index 00000000000..53ca5ba5b20
--- /dev/null
+++ b/Mac/scripts/fixgusidir.py
@@ -0,0 +1,89 @@
+# fixgusidir - Modify filenames in the CWGUSI source tree, so
+# that it can be put under CVS. Needed because there are files with slashes
+# in their name, which CVS does not approve of.
+#
+# Usage:
+# - On importing gusi in cvs:
+#   - Run the script after unpacking the gusi distribution. This creates
+#     _s_ files for all / files.
+#   - Remove all / files with "find file" or some such.
+#   - import the tree
+# - On checking out gusi:
+#   - After checkout, run the script to create / files for all _s_ files.
+# - After modifying stuff, or later checkouts:
+#   - Run the script. Conflicts between / and _s_ files will be reported.
+#   - Fix the problems by removing the outdated / or _s_ file.
+#   - Run the script again. Possibly do a cvs checkin.
+import macfs
+import os
+import sys
+import re
+
+# Substitution for slashes in filenames
+SUBST = '_s_'
+# Program to find those substitutions
+SUBSTPROG = re.compile(SUBST)
+
+def main():
+	if len(sys.argv) > 1:
+		gusidir = sys.argv[1]
+	else:
+		fss, ok = macfs.GetDirectory("CWGUSI source folder?")
+		if not ok: sys.exit(0)
+		gusidir = fss.as_pathname()
+	fixgusifolder(gusidir)
+	sys.exit(1)
+			
+def fixgusifolder(gusidir):
+	"""Synchronize files with / in their name with their _s_ counterparts"""
+	os.path.walk(gusidir, gusiwalk, None)
+	
+def gusiwalk(dummy, top, names):
+	"""Helper for fixgusifolder: convert a single directory full of files"""
+	# First remember names with slashes and with our slash-substitution
+	macnames = []
+	codenames = []
+	for name in names:
+		if '/' in name:
+			macnames.append(name)
+		if SUBSTPROG.search(name):
+			codenames.append(name)
+	# Next, check whether we need to copy any slash-files to subst-files
+	for name in macnames:
+		if os.path.isdir(name):
+			print '** Folder with slash in name cannot be handled!'
+			sys.exit(1)
+		othername = mac2codename(name)
+		if len(othername) > 31:
+			print '** Converted filename too long:', othername
+			sys.exit(1)
+		if othername in codenames:
+			codenames.remove(othername)
+		sync(os.path.join(top, name), os.path.join(top, othername))
+	# Now codenames contains only files that have no / equivalent
+	for name in codenames:
+		othername = code2macname(name)
+		sync(os.path.join(top, name), os.path.join(top, othername))
+		
+def mac2codename(name):
+	return re.sub('/', SUBST, name)
+	
+def code2macname(name):
+	return re.sub(SUBST, '/', name)
+	
+def sync(old, new):
+	if os.path.exists(new):
+		# Both exist. Check that they are indentical
+		d1 = open(old, 'rb').read()
+		d2 = open(new, 'rb').read()
+		if d1 == d2:
+			print '-- OK         ', old
+			return
+		print '** OUT-OF-SYNC', old
+	fp = open(new, 'wb')
+	fp.write(open(old, 'rb').read())
+	print '-- COPIED     ', old
+	
+if __name__ == '__main__':
+	main()
+