diff --git a/Modules/readline.c b/Modules/readline.c
index 488332f548e5fe3..a7e8bc2066a1ccc 100644
--- a/Modules/readline.c
+++ b/Modules/readline.c
@@ -1404,6 +1404,10 @@ setup_readline(readlinestate *mod_state)
     completer_word_break_characters =
         strdup(" \t\n`~!@#$%^&*()-=+[{]}\\|;:'\",<>/?");
         /* All nonalphanums except '.' */
+
+    if (!completer_word_break_characters) {
+        return -1;
+    }
 #ifdef WITH_EDITLINE
     // libedit uses rl_basic_word_break_characters instead of
     // rl_completer_word_break_characters as complete delimiter