--- a/build/autoconf/mozconfig2client-mk
+++ b/build/autoconf/mozconfig2client-mk
@@ -14,17 +14,27 @@ print_header() {
 # gmake
 # This file is automatically generated for client.mk.
 # Do not edit. Edit $FOUND_MOZCONFIG instead.
 
 EOF
 }
 
 ac_add_options() {
-  echo "# $* is used by configure (not client.mk)"
+  for _opt
+  do
+    case "$_opt" in
+    --target=*)
+      echo $_opt | sed s/--target/CONFIG_GUESS/
+      ;;
+    *)
+      echo "# $_opt is used by configure (not client.mk)"
+      ;;
+    esac
+  done
 }
 
 ac_add_app_options() {
   echo "# $* is used by configure (not client.mk)"
 }
 
 mk_add_options() {
   for _opt

--- a/python/mozbuild/mozbuild/base.py
+++ b/python/mozbuild/mozbuild/base.py
@@ -278,16 +278,20 @@ class MozbuildObject(ProcessExecutionMix
         if validate_exists and not os.path.exists(path):
             raise Exception('Binary expected at %s does not exist.' % path)
 
         return path
 
     @property
     def _config_guess(self):
         if self._config_guess_output is None:
+            make_extra = dict(m.split('=', 1) for m in self.mozconfig['make_extra'])
+            self._config_guess_output = make_extra.get('CONFIG_GUESS', None)
+
+        if self._config_guess_output is None:
             p = os.path.join(self.topsrcdir, 'build', 'autoconf',
                 'config.guess')
             args = self._normalize_command([p], True)
             self._config_guess_output = subprocess.check_output(args,
                 cwd=self.topsrcdir).strip()
 
         return self._config_guess_output
 

--- a/python/mozbuild/mozbuild/mozconfig_loader
+++ b/python/mozbuild/mozbuild/mozconfig_loader
@@ -7,16 +7,23 @@
 # This script is not meant to be called by users. Instead, some
 # higher-level driver invokes it and parses the machine-tailored output.
 
 set -e
 
 ac_add_options() {
   local opt
   for opt; do
+    case "$opt" in
+    --target=*)
+      echo "------BEGIN_MK_OPTION"
+      echo $opt | sed s/--target/CONFIG_GUESS/
+      echo "------END_MK_OPTION"
+      ;;
+    esac
     echo "------BEGIN_AC_OPTION"
     echo $opt
     echo "------END_AC_OPTION"
   done
 }
 
 ac_add_app_options() {
   local app