diff --git a/src/hb-subset-cff-common.hh b/src/hb-subset-cff-common.hh
index dbde64ce7..14d0b4341 100644
--- a/src/hb-subset-cff-common.hh
+++ b/src/hb-subset-cff-common.hh
@@ -565,7 +565,7 @@ 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);
+      parsed_charstrings[i].alloc (str.length / 2);
       subr_subset_param_t  param (&parsed_charstrings[i],
 				  &parsed_global_subrs,
 				  &parsed_local_subrs[fd],