diff --git a/src/hb-cff-interp-common.hh b/src/hb-cff-interp-common.hh
index 80857aec1..0a2302bdc 100644
--- a/src/hb-cff-interp-common.hh
+++ b/src/hb-cff-interp-common.hh
@@ -309,6 +309,8 @@ struct byte_str_t : hb_ubytes_t
   byte_str_t (const hb_ubytes_t &ub)	/* conversion from hb_ubytes_t */
     : hb_ubytes_t (ub) {}
   
+  void init (void) { str(); }
+  
   /* sub-string */
   byte_str_t sub_str (unsigned int offset, unsigned int len_) const
   { return byte_str_t (hb_ubytes_t::sub_array (offset, len_)); }
@@ -325,7 +327,7 @@ struct byte_str_ref_t
 
   void init ()
   {
-    str = byte_str_t ();
+    str.init ();
     offset = 0;
     error = false;
   }