diff --git a/fs/nfsd/blocklayout.c b/fs/nfsd/blocklayout.c
index e55b5242614da..31f3df193bdbb 100644
--- a/fs/nfsd/blocklayout.c
+++ b/fs/nfsd/blocklayout.c
@@ -290,7 +290,7 @@ static int nfsd4_scsi_identify_device(struct block_device *bdev,
 	return error;
 }
 
-#define NFSD_MDS_PR_KEY		0x0100000000000000
+#define NFSD_MDS_PR_KEY		0x0100000000000000ULL
 
 /*
  * We use the client ID as a unique key for the reservations.