diff --git a/libcxx/include/__bits b/libcxx/include/__bits
--- a/libcxx/include/__bits
+++ b/libcxx/include/__bits
@@ -76,7 +76,6 @@
 int __libcpp_ctz(unsigned long long __x) {
     unsigned long __where;
 #if defined(_LIBCPP_HAS_BITSCAN64)
-    (defined(_M_AMD64) || defined(__x86_64__))
   if (_BitScanForward64(&__where, __x))
     return static_cast<int>(__where);
 #else