diff --git a/fs/inotify.c b/fs/inotify.c
index 2fd97ef..a37e9fb 100644
--- a/fs/inotify.c
+++ b/fs/inotify.c
@@ -931,6 +931,7 @@
 	struct nameidata nd;
 	struct file *filp;
 	int ret, fput_needed;
+	int mask_add = 0;
 
 	filp = fget_light(fd, &fput_needed);
 	if (unlikely(!filp))
@@ -953,6 +954,9 @@
 	down(&inode->inotify_sem);
 	down(&dev->sem);
 
+	if (mask & IN_MASK_ADD)
+		mask_add = 1;
+
 	/* don't let user-space set invalid bits: we don't want flags set */
 	mask &= IN_ALL_EVENTS;
 	if (unlikely(!mask)) {
@@ -966,7 +970,10 @@
 	 */
 	old = inode_find_dev(inode, dev);
 	if (unlikely(old)) {
-		old->mask = mask;
+		if (mask_add)
+			old->mask |= mask;
+		else
+			old->mask = mask;
 		ret = old->wd;
 		goto out;
 	}
diff --git a/include/linux/inotify.h b/include/linux/inotify.h
index 93bb3af..ee5b239 100644
--- a/include/linux/inotify.h
+++ b/include/linux/inotify.h
@@ -47,6 +47,7 @@
 #define IN_MOVE			(IN_MOVED_FROM | IN_MOVED_TO) /* moves */
 
 /* special flags */
+#define IN_MASK_ADD		0x20000000	/* add to the mask of an already existing watch */
 #define IN_ISDIR		0x40000000	/* event occurred against dir */
 #define IN_ONESHOT		0x80000000	/* only send event once */