diff --git a/drivers/dax/device.c b/drivers/dax/device.c
index be8606457f27f02dc046ad1e8f02841742f8e4b4..aff2c1594220a9973e63894255d6873c2a9a53e7 100644
--- a/drivers/dax/device.c
+++ b/drivers/dax/device.c
@@ -19,6 +19,7 @@
 #include <linux/dax.h>
 #include <linux/fs.h>
 #include <linux/mm.h>
+#include <linux/mman.h>
 #include "dax-private.h"
 #include "dax.h"
 
@@ -540,6 +541,7 @@ static const struct file_operations dax_fops = {
 	.release = dax_release,
 	.get_unmapped_area = dax_get_unmapped_area,
 	.mmap = dax_mmap,
+	.mmap_supported_flags = MAP_SYNC,
 };
 
 static void dev_dax_release(struct device *dev)