diff --git a/clang/lib/Headers/intrin0.h b/clang/lib/Headers/intrin0.h
index 866c8896617d22a..6b01f3808652aa8 100644
--- a/clang/lib/Headers/intrin0.h
+++ b/clang/lib/Headers/intrin0.h
@@ -44,7 +44,7 @@ unsigned char _InterlockedCompareExchange128_rel(__int64 volatile *_Destination,
                                                  __int64 *_ComparandResult);
 #endif
 
-#ifdef __x86_64__ && !defined(__arm64ec__)
+#if defined(__x86_64__) && !defined(__arm64ec__)
 unsigned __int64 _umul128(unsigned __int64, unsigned __int64,
                           unsigned __int64 *);
 unsigned __int64 __shiftleft128(unsigned __int64 _LowPart,
diff --git a/clang/test/Headers/ms-intrin.cpp b/clang/test/Headers/ms-intrin.cpp
index cb7cd47956205c2..d630883e79d6a56 100644
--- a/clang/test/Headers/ms-intrin.cpp
+++ b/clang/test/Headers/ms-intrin.cpp
@@ -1,31 +1,31 @@
 // RUN: %clang_cc1 -triple i386-pc-win32 -target-cpu pentium4 \
 // RUN:     -fms-extensions -fms-compatibility -fms-compatibility-version=17.00 \
-// RUN:     -ffreestanding -fsyntax-only -Werror \
+// RUN:     -ffreestanding -fsyntax-only -Werror -Wsystem-headers \
 // RUN:     -isystem %S/Inputs/include %s
 
 // RUN: %clang_cc1 -triple i386-pc-win32 -target-cpu broadwell \
 // RUN:     -fms-extensions -fms-compatibility -fms-compatibility-version=17.00 \
-// RUN:     -ffreestanding -emit-obj -o /dev/null -Werror \
+// RUN:     -ffreestanding -emit-obj -o /dev/null -Werror -Wsystem-headers \
 // RUN:     -isystem %S/Inputs/include %s
 
 // RUN: %clang_cc1 -triple x86_64-pc-win32  \
 // RUN:     -fms-extensions -fms-compatibility -fms-compatibility-version=17.00 \
-// RUN:     -ffreestanding -emit-obj -o /dev/null -Werror \
+// RUN:     -ffreestanding -emit-obj -o /dev/null -Werror -Wsystem-headers \
 // RUN:     -isystem %S/Inputs/include %s
 
 // RUN: %clang_cc1 -triple thumbv7--windows \
 // RUN:     -fms-compatibility -fms-compatibility-version=17.00 \
-// RUN:     -ffreestanding -fsyntax-only -Werror \
+// RUN:     -ffreestanding -fsyntax-only -Werror -Wsystem-headers \
 // RUN:     -isystem %S/Inputs/include %s
 
 // RUN: %clang_cc1 -triple aarch64--windows \
 // RUN:     -fms-compatibility -fms-compatibility-version=17.00 \
-// RUN:     -ffreestanding -fsyntax-only -Werror \
+// RUN:     -ffreestanding -fsyntax-only -Werror -Wsystem-headers \
 // RUN:     -isystem %S/Inputs/include %s
 
 // RUN: %clang_cc1 -triple arm64ec--windows \
 // RUN:     -fms-compatibility -fms-compatibility-version=17.00 \
-// RUN:     -ffreestanding -fsyntax-only -Werror \
+// RUN:     -ffreestanding -fsyntax-only -Werror -Wsystem-headers \
 // RUN:     -isystem %S/Inputs/include %s
 
 // REQUIRES: x86-registered-target