diff --git a/src/hb-open-type-private.hh b/src/hb-open-type-private.hh
index a51b91e7eb1d21d2f1b9b7a45453b5a6fe1a4a6c..d11f3510b79c93e71ac04653f2277a5a4f174b77 100644
--- a/src/hb-open-type-private.hh
+++ b/src/hb-open-type-private.hh
@@ -293,7 +293,7 @@ struct Sanitizer
   retry:
     _hb_sanitize_init (&context, blob);
 
-    Type *t = &CAST (Type, context.start, 0);
+    Type *t = &CAST (Type, *DECONST_CHARP(context.start), 0);
 
     sane = t->sanitize (SANITIZE_ARG_INIT);
     if (sane) {