diff --git a/lib/krb5/error_string.c b/lib/krb5/error_string.c
index 89483681b..72b2e9a57 100644
--- a/lib/krb5/error_string.c
+++ b/lib/krb5/error_string.c
@@ -164,7 +164,7 @@ krb5_get_error_message(krb5_context context, krb5_error_code code)
  */
 
 void KRB5_LIB_FUNCTION
-krb5_free_error_message(krb5_context context, char *msg)
+krb5_free_error_message(krb5_context context, const char *msg)
 {
     free(msg);
 }