diff --git a/gnu/lib/libreadline/readline.c b/gnu/lib/libreadline/readline.c
index ee624c1e767..941243ed76f 100644
--- a/gnu/lib/libreadline/readline.c
+++ b/gnu/lib/libreadline/readline.c
@@ -278,7 +278,8 @@ readline (prompt)
       return ((char *)NULL);
     }
 
-  rl_visible_prompt_length = rl_expand_prompt (rl_prompt);
+  if (rl_prompt != NULL)
+    rl_visible_prompt_length = rl_expand_prompt (rl_prompt);
 
   rl_initialize ();
   rl_prep_terminal (_rl_meta_flag);