diff --git a/extensions/xt_quota2.c b/extensions/xt_quota2.c
index 8a2a509..b4d142e 100644
--- a/extensions/xt_quota2.c
+++ b/extensions/xt_quota2.c
@@ -82,7 +82,7 @@ quota_proc_write(struct file *file, const char __user *input,
                  size_t size, loff_t *loff)
 {
 	struct xt_quota_counter *e = PDE_DATA(file_inode(file));
-	char buf[sizeof("18446744073709551616")];
+	char buf[sizeof("+-18446744073709551616")];
 
 	if (size > sizeof(buf))
 		size = sizeof(buf);
@@ -92,9 +92,29 @@ quota_proc_write(struct file *file, const char __user *input,
 	if (size < sizeof(buf))
 		buf[size] = '\0';
 
-	spin_lock_bh(&e->lock);
-	e->quota = simple_strtoull(buf, NULL, 0);
-	spin_unlock_bh(&e->lock);
+	if (*buf == '+') {
+		int64_t temp = simple_strtoll(buf + 1, NULL, 0);
+		spin_lock_bh(&e->lock);
+		/* Do not let quota become negative if @tmp is very negative */
+		if (temp > 0 || -temp < e->quota)
+			e->quota += temp;
+		else
+			e->quota = 0;
+		spin_unlock_bh(&e->lock);
+	} else if (*buf == '-') {
+		int64_t temp = simple_strtoll(buf + 1, NULL, 0);
+		spin_lock_bh(&e->lock);
+		/* Do not let quota become negative if @tmp is very big */
+		if (temp < 0 || temp < e->quota)
+			e->quota -= temp;
+		else
+			e->quota = 0;
+		spin_unlock_bh(&e->lock);
+	} else {
+		spin_lock_bh(&e->lock);
+		e->quota = simple_strtoull(buf, NULL, 0);
+		spin_unlock_bh(&e->lock);
+	}
 	return size;
 }