diff --git a/test/lit.cfg b/test/lit.cfg
index 862a1bf6..0c74a7d0 100644
--- a/test/lit.cfg
+++ b/test/lit.cfg
@@ -276,8 +276,13 @@ config.test_format = LibcxxTestFormat(
     ld_flags = ['-nodefaultlibs'] + library_paths + ['-lc++'] + libraries,
     exec_env = exec_env)
 
-config.target_triple = lit.params.get(
-    'target_triple', 'unknown-unknown-unknown')
+# Get or infer the target triple.
+config.target_triple = lit.params.get('target_triple', None)
+# If no target triple was given, try to infer it from the compiler under test.
+if config.target_triple is None:
+    config.target_triple = lit.util.capture(
+        [cxx_under_test, '-dumpmachine']).strip()
+    lit.note("inferred target triple as: %r" % (config.target_triple,))
 
 # 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