diff --git a/login-utils/su.c b/login-utils/su.c
index 27a56d505..d7460859f 100644
--- a/login-utils/su.c
+++ b/login-utils/su.c
@@ -180,7 +180,7 @@ static struct option const longopts[] =
 /* Add VAL to the environment, checking for out of memory errors.  */
 
 static void
-xputenv (const char *val)
+xputenv (char *val)
 {
   if (putenv (val))
     xalloc_die ();