diff --git a/libguile/posix-w32.h b/libguile/posix-w32.h
index 83860ff85..ba1dff2dc 100644
--- a/libguile/posix-w32.h
+++ b/libguile/posix-w32.h
@@ -24,7 +24,7 @@
 #ifndef WIN32_LEAN_AND_MEAN
 #define WIN32_LEAN_AND_MEAN
 #endif
-#include <Windows.h>
+#include <windows.h>
 #endif
 #include <string.h>
 #include "libguile/scm.h"