diff --git a/include/c11/threads_win32.h b/include/c11/threads_win32.h
index 8c014fab45c..1b740d58176 100644
--- a/include/c11/threads_win32.h
+++ b/include/c11/threads_win32.h
@@ -54,7 +54,9 @@ Configuration macro:
 #endif
 #define EMULATED_THREADS_TSS_DTOR_SLOTNUM 64  // see TLS_MINIMUM_AVAILABLE
 
-
+#ifndef WIN32_LEAN_AND_MEAN
+#define WIN32_LEAN_AND_MEAN 1
+#endif
 #include <windows.h>
 
 // check configuration
diff --git a/src/util/memstream.h b/src/util/memstream.h
index 2d4be8257c1..0bed1132559 100644
--- a/src/util/memstream.h
+++ b/src/util/memstream.h
@@ -31,6 +31,9 @@
 #include <stdbool.h>
 #include <stdio.h>
 #ifdef _WIN32
+#ifndef WIN32_LEAN_AND_MEAN
+#define WIN32_LEAN_AND_MEAN 1
+#endif
 #include <windows.h>
 #endif