--- a/build/moz.configure/rust.configure
+++ b/build/moz.configure/rust.configure
@@ -278,9 +280,10 @@
             die("Don't know how to translate {} for rustc".format(
                 host_or_target.alias))
 
+        fixed_alias = os.environ['RUST_TARGET']
         # Check to see whether our rustc has a reasonably functional stdlib
         # for our chosen target.
-        target_arg = '--target=' + rustc_target.alias
+        target_arg = '--target=' + fixed_alias
         in_fd, in_path = mkstemp(prefix='conftest', suffix='.rs')
         out_fd, out_path = mkstemp(prefix='conftest', suffix='.rlib')
         os.close(out_fd)
@@ -317,7 +320,7 @@
             os.remove(out_path)
 
         # This target is usable.
-        return rustc_target.alias
+        return fixed_alias
 
     return rust_target