diff --git a/lib/System/RWMutex.cpp b/lib/System/RWMutex.cpp
index deb04709d82..be41ee6847d 100644
--- a/lib/System/RWMutex.cpp
+++ b/lib/System/RWMutex.cpp
@@ -12,6 +12,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Config/config.h"
+#include "llvm/Support/Compiler.h"
 #include "llvm/System/RWMutex.h"
 #include <cstring>
 
@@ -72,8 +73,7 @@ RWMutexImpl::RWMutexImpl()
 #endif
 
     // Initialize the rwlock
-    int errorcode = pthread_rwlock_init(rwlock, NULL);
-    (void)errorcode;
+    int ATTRIBUTE_UNUSED errorcode = pthread_rwlock_init(rwlock, NULL);
     assert(errorcode == 0);
 
     // Assign the data member
diff --git a/lib/System/Win32/ThreadLocal.inc b/lib/System/Win32/ThreadLocal.inc
index e7e3cb7ce11..b13c119c4e6 100644
--- a/lib/System/Win32/ThreadLocal.inc
+++ b/lib/System/Win32/ThreadLocal.inc
@@ -17,6 +17,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "Win32.h"
+#include "llvm/Support/Compiler.h"
 #include "llvm/System/ThreadLocal.h"
 
 namespace llvm {
@@ -42,9 +43,8 @@ const void* ThreadLocalImpl::getInstance() {
 
 void ThreadLocalImpl::setInstance(const void* d){
   DWORD* tls = static_cast<DWORD*>(data);
-  int errorcode = TlsSetValue(*tls, const_cast<void*>(d));
+  int ATTRIBUTE_UNUSED errorcode = TlsSetValue(*tls, const_cast<void*>(d));
   assert(errorcode != 0);
-  (void)errorcode;
 }
 
 void ThreadLocalImpl::removeInstance() {