diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index b12fc82e34bae7c87ba44e6c97e24585d61ec2da..03670d4cd6ed902dafeccd9ebabd2129160e4abe 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -2775,8 +2775,22 @@ static int btrfs_finish_ordered_io(struct btrfs_ordered_extent *ordered_extent)
 			unwritten_start += logical_len;
 		clear_extent_uptodate(io_tree, unwritten_start, end, NULL);
 
-		/* Drop the cache for the part of the extent we didn't write. */
-		btrfs_drop_extent_cache(BTRFS_I(inode), unwritten_start, end, 0);
+		/*
+		 * Drop extent maps for the part of the extent we didn't write.
+		 *
+		 * We have an exception here for the free_space_inode, this is
+		 * because when we do btrfs_get_extent() on the free space inode
+		 * we will search the commit root.  If this is a new block group
+		 * we won't find anything, and we will trip over the assert in
+		 * writepage where we do ASSERT(em->block_start !=
+		 * EXTENT_MAP_HOLE).
+		 *
+		 * Theoretically we could also skip this for any NOCOW extent as
+		 * we don't mess with the extent map tree in the NOCOW case, but
+		 * for now simply skip this if we are the free space inode.
+		 */
+		if (!btrfs_is_free_space_inode(BTRFS_I(inode)))
+			btrfs_drop_extent_cache(BTRFS_I(inode), unwritten_start, end, 0);
 
 		/*
 		 * If the ordered extent had an IOERR or something else went