diff --git a/third_party/vaca/src/win32/MutexImpl.h b/third_party/vaca/src/win32/MutexImpl.h
index 143ad2238..021a35e69 100644
--- a/third_party/vaca/src/win32/MutexImpl.h
+++ b/third_party/vaca/src/win32/MutexImpl.h
@@ -32,6 +32,7 @@
 #ifndef _WIN32_WINNT
 #define _WIN32_WINNT 0x0400
 #endif
+#define WIN32_LEAN_AND_MEAN
 #include <windows.h>
 
 class Vaca::Mutex::MutexImpl