diff --git a/lib/env.c b/lib/env.c
index dc35c54d..6d6b1370 100644
--- a/lib/env.c
+++ b/lib/env.c
@@ -192,8 +192,7 @@ void set_env (int argc, char *const *argv)
 			}
 
 			if (NULL != *p) {
-				strncpy (variable, *argv, (size_t)(cp - *argv));
-				variable[cp - *argv] = '\0';
+				stpcpy(mempcpy(variable, *argv, (size_t)(cp - *argv)), "");
 				printf (_("You may not change $%s\n"),
 					variable);
 				continue;