--- a/mach
+++ b/mach
@@ -7,19 +7,19 @@ from __future__ import print_function, u
 
 import os
 import platform
 import sys
 
 # Ensure we are running Python 2.7+. We put this check here so we generate a
 # user-friendly error message rather than a cryptic stack trace on module
 # import.
-if sys.version_info[0] == 2 and sys.version_info[1] < 7:
-    print('Python 2.7 or above is required to run mach.')
-    print('You are running', platform.python_version())
+if sys.version_info[0] != 2 or sys.version_info[1] < 7:
+    print('Python 2.7 or above (but not Python 3) is required to run mach.')
+    print('You are running Python', platform.python_version())
     sys.exit(1)
 
 # TODO Bug 794506 Integrate with the in-tree virtualenv configuration.
 SEARCH_PATHS = [
     'python/mach',
     'python/mozboot',
     'python/mozbuild',
     'build',