diff --git a/lib/charms/defm/expander.ex b/lib/charms/defm/expander.ex
index fb0b468..2c4b87c 100644
--- a/lib/charms/defm/expander.ex
+++ b/lib/charms/defm/expander.ex
@@ -500,7 +500,7 @@ defmodule Charms.Defm.Expander do
                   term_ptr = Pointer.allocate(Term.t())
                   size = String.length(attr)
                   buffer_ptr = Pointer.allocate(i8(), size)
-                  buffer = ptr_to_memref(buffer_ptr)
+                  buffer = ptr_to_memref(buffer_ptr, size)
                   memref.copy(attr, buffer)
                   zero = const 0 :: i32()
                   enif_binary_to_term(unquote(env_var), buffer_ptr, size, term_ptr, zero)