Formalize buffer var allocations
diff --git a/src/hb-private.hh b/src/hb-private.hh
index 9482795..6c19d37 100644
--- a/src/hb-private.hh
+++ b/src/hb-private.hh
@@ -36,6 +36,7 @@
 #include "hb-common.h"
 
 #include <stdlib.h>
+#include <stddef.h>
 #include <string.h>
 #include <assert.h>