diff --git a/Process.c b/Process.c
index d80ad796..acb7a768 100644
--- a/Process.c
+++ b/Process.c
@@ -426,7 +426,7 @@ void Process_display(const Object* cast, RichString* out) {
       }
    }
 
-   assert(out->chlen > 0);
+   assert(RichString_size(out) > 0);
 }
 
 void Process_done(Process* this) {