diff --git a/src/hb-cff-interp-common.hh b/src/hb-cff-interp-common.hh
index 058dc0cdd..1cd165615 100644
--- a/src/hb-cff-interp-common.hh
+++ b/src/hb-cff-interp-common.hh
@@ -520,6 +520,11 @@ struct parsed_values_t
   }
   void fini () { values.fini (); }
 
+  void alloc (unsigned n)
+  {
+    values.alloc (n);
+  }
+
   void add_op (op_code_t op, const byte_str_ref_t& str_ref = byte_str_ref_t ())
   {
     VAL *val = values.push ();
diff --git a/src/hb-subset-cff-common.hh b/src/hb-subset-cff-common.hh
index e3fae0850..0405b35bf 100644
--- a/src/hb-subset-cff-common.hh
+++ b/src/hb-subset-cff-common.hh
@@ -569,6 +569,7 @@ struct subr_subsetter_t
       ENV env (str, acc, fd);
       cs_interpreter_t<ENV, OPSET, subr_subset_param_t> interp (env);
 
+      parsed_charstrings[i].alloc (str.length);
       subr_subset_param_t  param (&parsed_charstrings[i],
 				  &parsed_global_subrs,
 				  &parsed_local_subrs[fd],