--- a/build/moz.configure/init.configure
+++ b/build/moz.configure/init.configure
@@ -56,32 +56,38 @@ def check_build_environment(help, dist):
             '  *   To clean up the source tree:\n'
             '  *     1. cd %s\n'
             '  *     2. gmake distclean\n'
             '  ***'
             % ('\n  '.join(conflict_files), topsrcdir)
         )
 
 
+option(env='OLD_CONFIGURE', nargs=1, help='Path to the old configure script')
+
 option(env='MOZ_CURRENT_PROJECT', nargs=1, help='Current build project')
 option(env='MOZCONFIG', nargs=1, help='Mozconfig location')
 
 # Read user mozconfig
 # ==============================================================
 # Note: the dependency on --help is only there to always read the mozconfig,
 # even when --help is passed. Without this dependency, the function wouldn't
 # be called when --help is passed, and the mozconfig wouldn't be read.
-@depends('MOZ_CURRENT_PROJECT', 'MOZCONFIG', check_build_environment, '--help')
+@depends('MOZ_CURRENT_PROJECT', 'MOZCONFIG', 'OLD_CONFIGURE',
+         check_build_environment, '--help')
 @advanced
-def mozconfig(current_project, mozconfig,  build_env, help):
+def mozconfig(current_project, mozconfig, old_configure, build_env, help):
     from mozbuild.mozconfig import MozconfigLoader
 
+    if not old_configure:
+        error('The OLD_CONFIGURE environment variable must be set')
+
     # Don't read the mozconfig for the js configure (yay backwards
     # compatibility)
-    if build_env['TOPOBJDIR'].endswith('/js/src'):
+    if os.path.dirname(old_configure[0]).endswith('/js/src'):
         return {'path': None}
 
     loader = MozconfigLoader(build_env['TOPSRCDIR'])
     current_project = current_project[0] if current_project else None
     mozconfig = mozconfig[0] if mozconfig else None
     mozconfig = loader.find_mozconfig(env={'MOZCONFIG': mozconfig})
     mozconfig = loader.read_mozconfig(mozconfig, moz_build_app=current_project)
 

--- a/build/moz.configure/old.configure
+++ b/build/moz.configure/old.configure
@@ -52,18 +52,16 @@ def autoconf(mozconfig, autoconf):
 
     if not autoconf:
         error('Could not find autoconf 2.13')
 
     set_config('AUTOCONF', autoconf)
     return autoconf
 
 
-option(env='OLD_CONFIGURE', nargs=1, help='Path to the old configure script')
-
 @depends('OLD_CONFIGURE', mozconfig, autoconf, check_build_environment, shell,
          virtualenv_python, compile_environment, build_project,
          extra_old_configure_args, '--with-external-source-dir',
          '--enable-shared-js', old_configure_assignments)
 @advanced
 def prepare_configure(old_configure, mozconfig, autoconf, build_env, shell,
                       python, compile_env, build_project,
                       extra_old_configure_args, external_source_dir,
@@ -72,19 +70,16 @@ def prepare_configure(old_configure, moz
     import itertools
     import subprocess
     import sys
     # Import getmtime without overwriting the sandbox os.path.
     from os.path import getmtime
 
     from mozbuild.shellutil import quote
 
-    if not old_configure:
-        error('The OLD_CONFIGURE environment variable must be set')
-
     # os.path.abspath in the sandbox will ensure forward slashes on Windows,
     # which is actually necessary because this path actually ends up literally
     # as $0, and backslashes there breaks autoconf's detection of the source
     # directory.
     old_configure = os.path.abspath(old_configure[0])
 
     refresh = True
     if os.path.exists(old_configure):