diff --git a/libcxx/utils/libcxx/test/features.py b/libcxx/utils/libcxx/test/features.py
--- a/libcxx/utils/libcxx/test/features.py
+++ b/libcxx/utils/libcxx/test/features.py
@@ -41,14 +41,11 @@
                                                                  sys.platform.lower().strip() == 'darwin'), # TODO: this doesn't handle cross-compiling to Apple platforms.
   Feature(name='objective-c++',                 when=lambda cfg: hasCompileFlag(cfg, '-xobjective-c++ -fobjc-arc')),
 
-  # Note: We use a custom modules cache path to make sure that we don't reuse
-  #       the default one, which can be shared across builds. This is important
-  #       because we define macros in headers files, and a change in these macros
-  #       doesn't seem to invalidate modules cache entries, which means we could
-  #       build against now-invalid cached headers from a previous build.
+  # NOTE: We make sure that Clang considers system headers for invalidating the
+  # modules cache, otherwise we could be using stale versions of the headers.
   Feature(name='modules-support',
           when=lambda cfg: hasCompileFlag(cfg, '-fmodules'),
-          actions=lambda cfg: [AddCompileFlag('-fmodules-cache-path=%t/ModuleCache')]),
+          actions=lambda cfg: [AddCompileFlag('-fmodules-validate-system-headers')]),
 
   Feature(name='non-lockfree-atomics',
           when=lambda cfg: sourceBuilds(cfg, """