tests/hghave.py

--- a/tests/hghave.py	Wed Aug 29 09:59:08 2018 -0700
+++ b/tests/hghave.py	Wed Jul 25 13:45:28 2018 -0400
@@ -631,7 +631,7 @@
 
 @check("py3exe", "a Python 3.x interpreter is available")
 def has_python3exe():
-    return 'PYTHON3' in os.environ
+    return matchoutput('python3 -V', br'^Python 3.(5|6|7|8|9)')
 
 @check("py3pygments", "Pygments available on Python 3.x")
 def has_py3pygments():