diff --git a/windows/alloca.h b/windows/alloca.h
index f8fa6f17a0..1cf7722669 100644
--- a/windows/alloca.h
+++ b/windows/alloca.h
@@ -1 +1,3 @@
-#include <malloc.h>
+// Compatibility header to workaround lack of native alloca.h in some
+// Windows toolchains.
+#include <malloc.h>