diff --git a/libcxx/test/support/filesystem_test_helper.h b/libcxx/test/support/filesystem_test_helper.h
--- a/libcxx/test/support/filesystem_test_helper.h
+++ b/libcxx/test/support/filesystem_test_helper.h
@@ -31,8 +31,12 @@
 # include <sys/un.h>
 #endif
 
-_LIBCPP_PUSH_MACROS
-#include <__undef_macros>
+#ifdef _WIN32
+// If built without -DNOMINMAX, Windows system headers can pollute the
+// namespace with min/max defines that break standard C++.
+#undef min
+#undef max
+#endif
 
 namespace utils {
 #ifdef _WIN32
@@ -736,6 +740,4 @@
   return fs::path();
 }
 
-_LIBCPP_POP_MACROS
-
 #endif /* FILESYSTEM_TEST_HELPER_H */