diff --git a/libcxx/test/lit.cfg b/libcxx/test/lit.cfg
index 30d4416099e0..862a1bf627e8 100644
--- a/libcxx/test/lit.cfg
+++ b/libcxx/test/lit.cfg
@@ -278,3 +278,11 @@ config.test_format = LibcxxTestFormat(
 
 config.target_triple = lit.params.get(
     'target_triple', 'unknown-unknown-unknown')
+
+# Write an "available feature" that combines the triple when use_system_lib is
+# enabled. This is so that we can easily write XFAIL markers for tests that are
+# known to fail with versions of libc++ as were shipped with a particular
+# triple.
+if use_system_lib:
+    config.available_features.add('with_system_lib=%s' % (
+            config.target_triple,))