diff --git a/src/hb-private.hh b/src/hb-private.hh
index b735c0d32d3..36bb4dd021f 100644
--- a/src/hb-private.hh
+++ b/src/hb-private.hh
@@ -53,6 +53,10 @@
 #include <errno.h>
 #include <stdarg.h>
 
+#ifdef _MSC_VER
+#include <windows.h> /* ensure DEFINE_ENUM_FLAG_OPERATORS is defined */
+#endif
+
 
 /* Compile-time custom allocator support. */