--- a/unixSoft/bin/havepatch
+++ b/unixSoft/bin/havepatch
@@ -1,10 +1,16 @@
 #!/usr/bin/env python
 """Detect if a patch is already applied in a Mercurial repository."""
+import json
 import os
 import re
 import subprocess
 import sys
 
+# Always load hg libraries from the hg we can find on $PATH.
+hglib = json.loads(subprocess.check_output(
+    ['hg', 'debuginstall', '-Tjson']))[0]['hgmodules']
+sys.path.insert(0, os.path.dirname(hglib))
+
 from mercurial import util
 
 def main(argv):