--- a/build/moz.configure/init.configure
+++ b/build/moz.configure/init.configure
@@ -333,24 +333,25 @@ def mozconfig_options(mozconfig, wanted_
 # Mozilla-Build
 # ==============================================================
 option(env='MOZILLABUILD', nargs=1,
        help='Path to Mozilla Build (Windows-only)')
 
 # It feels dirty replicating this from python/mozbuild/mozbuild/mozconfig.py,
 # but the end goal being that the configure script would go away...
 @depends('MOZILLABUILD')
+@checking('for a shell')
 @imports('sys')
 def shell(mozillabuild):
     shell = 'sh'
     if mozillabuild:
         shell = mozillabuild[0] + '/msys/bin/sh'
     if sys.platform == 'win32':
         shell = shell + '.exe'
-    return shell
+    return find_program(shell)
 
 
 # Host and target systems
 # ==============================================================
 option('--host', nargs=1, help='Define the system type performing the build')
 
 option('--target', nargs=1,
        help='Define the system type where the resulting executables will be '

--- a/build/moz.configure/old.configure
+++ b/build/moz.configure/old.configure
@@ -9,16 +9,17 @@
 def encoded_open(path, mode):
     encoding = 'mbcs' if sys.platform == 'win32' else 'utf-8'
     return codecs.open(path, mode, encoding)
 
 
 option(env='AUTOCONF', nargs=1, help='Path to autoconf 2.13')
 
 @depends(mozconfig, 'AUTOCONF')
+@checking('for autoconf')
 @imports('re')
 def autoconf(mozconfig, autoconf):
     mozconfig_autoconf = None
     if mozconfig['path']:
         make_extra = mozconfig['make_extra']
         if make_extra:
             for assignment in make_extra:
                 m = re.match('(?:export\s+)?AUTOCONF\s*:?=\s*(.+)$',