diff -r c8cdc2400643 Modules/readline.c
--- a/Modules/readline.c	Sun May 05 11:34:21 2013 -0500
+++ b/Modules/readline.c	Sun May 05 15:42:56 2013 -0700
@@ -70,6 +70,9 @@
                                    int num_matches, int max_length);
 #endif
 
+/* Memory allocated for rl_completer_word_break_characters. */
+static char *readlinestate_completer_word_break_characters;
+
 /* Exported function to send one line to readline's init file parser */
 
 static PyObject *
@@ -371,8 +374,12 @@
     if(!PyArg_ParseTuple(args, "s:set_completer_delims", &break_chars)) {
         return NULL;
     }
-    free((void*)rl_completer_word_break_characters);
-    rl_completer_word_break_characters = strdup(break_chars);
+    /* Keep a reference to the allocated memory in the module state in case
+       some other module modifies rl_completer_word_break_characters. */
+    free((void*)readlinestate_completer_word_break_characters);
+    readlinestate_completer_word_break_characters =
+        rl_completer_word_break_characters =
+        strdup(break_chars);
     Py_RETURN_NONE;
 }
 
@@ -918,7 +925,8 @@
     /* Set our completion function */
     rl_attempted_completion_function = (CPPFunction *)flex_complete;
     /* Set Python word break characters */
-    rl_completer_word_break_characters =
+    readlinestate_completer_word_break_characters =
+        rl_completer_word_break_characters =
         strdup(" \t\n`~!@#$%^&*()-=+[{]}\\|;:'\",<>/?");
         /* All nonalphanums except '.' */