--- a/python/mozboot/mozboot/windows.py
+++ b/python/mozboot/mozboot/windows.py
@@ -34,18 +34,20 @@ class WindowsBootstrapper(BaseBootstrapp
     MOBILE_ANDROID_COMMON_PACKAGES = [
         'wget'
     ]
 
     def __init__(self, **kwargs):
         if 'MOZ_WINDOWS_BOOTSTRAP' not in os.environ or os.environ['MOZ_WINDOWS_BOOTSTRAP'] != '1':
             raise NotImplementedError('Bootstrap support for Windows is under development. For now, use MozillaBuild '
                                       'to set up a build environment on Windows. If you are testing Windows Bootstrap support, '
-                                      'try `export MOZ_WINDOWS_BOOTSTRAP=1`')
+                                      'try `export MOZ_WINDOWS_BOOTSTRAP=1`. Also add `. $TOPSRCDIR/build/mozconfig.msys` to '
+                                      'your `.mozconfig`.')
         BaseBootstrapper.__init__(self, **kwargs)
+
         if not self.which('pacman'):
             raise NotImplementedError('The Windows bootstrapper only works with msys2 with pacman. Get msys2 at '
                                       'http://msys2.github.io/')
         print 'Using an experimental bootstrapper for Windows.'
 
     def which(self, name):
         return BaseBootstrapper.which(self, name + '.exe')