diff --git a/extensions/xt_quota2.c b/extensions/xt_quota2.c
index aa00207..52c88a1 100644
--- a/extensions/xt_quota2.c
+++ b/extensions/xt_quota2.c
@@ -76,6 +76,8 @@ quota_proc_write(struct file *file, const char __user *input,
 	if (copy_from_user(buf, input, size) != 0)
 		return -EFAULT;
 	buf[sizeof(buf)-1] = '\0';
+	if (size < sizeof(buf))
+		buf[size] = '\0';
 
 	spin_lock_bh(&e->lock);
 	e->quota = simple_strtoull(buf, NULL, 0);