diff --git a/fs/timerfd.c b/fs/timerfd.c
index 6a123b8ff3f5605735255f7ccaf084af547743dd..b042bd7034b1fc74d6cd6399e24b3a2057689a2f 100644
--- a/fs/timerfd.c
+++ b/fs/timerfd.c
@@ -186,10 +186,9 @@ SYSCALL_DEFINE2(timerfd_create, int, clockid, int, flags)
 	BUILD_BUG_ON(TFD_CLOEXEC != O_CLOEXEC);
 	BUILD_BUG_ON(TFD_NONBLOCK != O_NONBLOCK);
 
-	if (flags & ~(TFD_CLOEXEC | TFD_NONBLOCK))
-		return -EINVAL;
-	if (clockid != CLOCK_MONOTONIC &&
-	    clockid != CLOCK_REALTIME)
+	if ((flags & ~TFD_CREATE_FLAGS) ||
+	    (clockid != CLOCK_MONOTONIC &&
+	     clockid != CLOCK_REALTIME))
 		return -EINVAL;
 
 	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
@@ -201,7 +200,7 @@ SYSCALL_DEFINE2(timerfd_create, int, clockid, int, flags)
 	hrtimer_init(&ctx->tmr, clockid, HRTIMER_MODE_ABS);
 
 	ufd = anon_inode_getfd("[timerfd]", &timerfd_fops, ctx,
-			       flags & (O_CLOEXEC | O_NONBLOCK));
+			       flags & TFD_SHARED_FCNTL_FLAGS);
 	if (ufd < 0)
 		kfree(ctx);
 
@@ -219,7 +218,8 @@ SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
 	if (copy_from_user(&ktmr, utmr, sizeof(ktmr)))
 		return -EFAULT;
 
-	if (!timespec_valid(&ktmr.it_value) ||
+	if ((flags & ~TFD_SETTIME_FLAGS) ||
+	    !timespec_valid(&ktmr.it_value) ||
 	    !timespec_valid(&ktmr.it_interval))
 		return -EINVAL;
 
diff --git a/include/linux/timerfd.h b/include/linux/timerfd.h
index 86cb0501d3e20428b749eb2156bf5abc301e1c20..2d0792983f8c2d7500b8e7a595b48b36ff6579f2 100644
--- a/include/linux/timerfd.h
+++ b/include/linux/timerfd.h
@@ -11,13 +11,21 @@
 /* For O_CLOEXEC and O_NONBLOCK */
 #include <linux/fcntl.h>
 
-/* Flags for timerfd_settime.  */
+/*
+ * CAREFUL: Check include/asm-generic/fcntl.h when defining
+ * new flags, since they might collide with O_* ones. We want
+ * to re-use O_* flags that couldn't possibly have a meaning
+ * from eventfd, in order to leave a free define-space for
+ * shared O_* flags.
+ */
 #define TFD_TIMER_ABSTIME (1 << 0)
-
-/* Flags for timerfd_create.  */
 #define TFD_CLOEXEC O_CLOEXEC
 #define TFD_NONBLOCK O_NONBLOCK
 
+#define TFD_SHARED_FCNTL_FLAGS (TFD_CLOEXEC | TFD_NONBLOCK)
+/* Flags for timerfd_create.  */
+#define TFD_CREATE_FLAGS TFD_SHARED_FCNTL_FLAGS
+/* Flags for timerfd_settime.  */
+#define TFD_SETTIME_FLAGS TFD_TIMER_ABSTIME
 
 #endif /* _LINUX_TIMERFD_H */
-