diff --git a/include/linux/dax.h b/include/linux/dax.h
index 70600b6..aa14893 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -3,6 +3,7 @@
 
 #include <linux/fs.h>
 #include <linux/mm.h>
+#include <linux/radix-tree.h>
 #include <asm/pgtable.h>
 
 /* We use lowest available exceptional entry bit for locking */