diff --git a/port/win/io_win.cc b/port/win/io_win.cc
index e050d69dd..c433e5e52 100644
--- a/port/win/io_win.cc
+++ b/port/win/io_win.cc
@@ -1025,7 +1025,12 @@ Status WinRandomRWFile::Close() {
 //////////////////////////////////////////////////////////////////////////
 /// WinMemoryMappedBufer
 WinMemoryMappedBuffer::~WinMemoryMappedBuffer() {
-  BOOL ret = FALSE;
+  BOOL ret
+#if defined(_MSC_VER)
+    = FALSE;
+#else
+    __attribute__((__unused__));
+#endif
   if (base_ != nullptr) {
     ret = ::UnmapViewOfFile(base_);
     assert(ret);
diff --git a/port/win/win_thread.cc b/port/win/win_thread.cc
index 9a976e2c6..34e54f301 100644
--- a/port/win/win_thread.cc
+++ b/port/win/win_thread.cc
@@ -138,7 +138,12 @@ void WindowsThread::join() {
       "WaitForSingleObjectFailed: thread join");
   }
 
-  BOOL rc;
+  BOOL rc
+#if defined(_MSC_VER)
+    = FALSE;
+#else
+    __attribute__((__unused__));
+#endif
   rc = CloseHandle(reinterpret_cast<HANDLE>(data_->handle_));
   assert(rc != 0);
   data_->handle_ = 0;
diff --git a/util/status.cc b/util/status.cc
index 0b1b24935..d75f9271e 100644
--- a/util/status.cc
+++ b/util/status.cc
@@ -21,7 +21,12 @@ const char* Status::CopyState(const char* state) {
 #ifdef OS_WIN
   const size_t cch = std::strlen(state) + 1;  // +1 for the null terminator
   char* result = new char[cch];
-  errno_t ret;
+  errno_t ret
+#if defined(_MSC_VER)
+    ;
+#else
+    __attribute__((__unused__));
+#endif
   ret = strncpy_s(result, cch, state, cch - 1);
   result[cch - 1] = '\0';
   assert(ret == 0);