diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 30cf917a58e92c4f75d1bf054a7d4eac26d76f86..81e98a457130f8e6ee52d3f70b54c3eda1dd1663 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -4662,7 +4662,7 @@ int extent_fiemap(struct btrfs_inode *inode, struct fiemap_extent_info *fieinfo,
 		  u64 start, u64 len)
 {
 	int ret = 0;
-	u64 off = start;
+	u64 off;
 	u64 max = start + len;
 	u32 flags = 0;
 	u32 found_type;
@@ -4698,6 +4698,11 @@ int extent_fiemap(struct btrfs_inode *inode, struct fiemap_extent_info *fieinfo,
 		goto out_free_ulist;
 	}
 
+	/*
+	 * We can't initialize that to 'start' as this could miss extents due
+	 * to extent item merging
+	 */
+	off = 0;
 	start = round_down(start, btrfs_inode_sectorsize(inode));
 	len = round_up(max, btrfs_inode_sectorsize(inode)) - start;