--- a/build/moz.configure/keyfiles.configure
+++ b/build/moz.configure/keyfiles.configure
@@ -31,18 +31,22 @@ def keyfile(desc, help=None, callback=la
                 pass
         return no_key
 
     return keyfile
 
 
 @template
 def simple_keyfile(desc):
-    set_config('MOZ_%s_KEY' % desc.upper().replace(' ', '_'),
-               keyfile(desc))
+    value = keyfile(desc)
+    set_config('MOZ_%s_KEY' % desc.upper().replace(' ', '_'), value)
+    # Only really required for MOZ_ADJUST_SDK_KEY currently still used in
+    # old-configure.
+    add_old_configure_assignment('MOZ_%s_KEY' % desc.upper().replace(' ', '_'),
+                                 value)
 
 
 @template
 def id_and_secret_keyfile(desc):
     def id_and_secret(value):
         if value.startswith('no-') and value.endswith('-key'):
             id = value[:-3] + 'clientid'
             secret = value