* time it is called after a failed call to a krb5 function using the
* same context, and only when the error code passed in is the same as
* that returned by the krb5 function. Future versions may return the
- * same string for the second and following calls.
+ * same string for the second and following calls. This function never
+ * returns NULL, so its result may be used unconditionally as a C
+ * string.
*
* The string returned by this function must be freed using
* krb5_free_error_message.