--- a/build/moz.configure/init.configure
+++ b/build/moz.configure/init.configure
@@ -128,18 +128,23 @@ def old_configure_assignments(help):
 def extra_old_configure_args(help):
     return []
 
 @template
 def add_old_configure_assignment(var, value):
     @depends(old_configure_assignments)
     @advanced
     def add_assignment(assignments):
-        from mozbuild.shellutil import quote
-        assignments.append('%s=%s' % (var, quote(value)))
+        if value is True:
+            assignments.append('%s=1' % var)
+        elif value is False:
+            assignments.append('%s=' % var)
+        else:
+            from mozbuild.shellutil import quote
+            assignments.append('%s=%s' % (var, quote(value)))
 
 @template
 def add_old_configure_arg(arg):
     @depends(extra_old_configure_args)
     def add_arg(args):
         args.append(arg)