diff --git a/fs/btrfs/block-rsv.c b/fs/btrfs/block-rsv.c
index 4cbf38616620..a47c8b450996 100644
--- a/fs/btrfs/block-rsv.c
+++ b/fs/btrfs/block-rsv.c
@@ -384,17 +384,19 @@ void btrfs_update_global_block_rsv(struct btrfs_fs_info *fs_info)
 
 	/*
 	 * But we also want to reserve enough space so we can do the fallback
-	 * global reserve for an unlink, which is an additional 5 items (see the
-	 * comment in __unlink_start_trans for what we're modifying.)
+	 * global reserve for an unlink, which is an additional
+	 * BTRFS_UNLINK_METADATA_UNITS items.
 	 *
 	 * But we also need space for the delayed ref updates from the unlink,
-	 * so its 10, 5 for the actual operation, and 5 for the delayed ref
-	 * updates.
+	 * so add BTRFS_UNLINK_METADATA_UNITS units for delayed refs, one for
+	 * each unlink metadata item.
 	 */
-	min_items += 10;
+	min_items += BTRFS_UNLINK_METADATA_UNITS;
 
 	num_bytes = max_t(u64, num_bytes,
-			  btrfs_calc_insert_metadata_size(fs_info, min_items));
+			  btrfs_calc_insert_metadata_size(fs_info, min_items) +
+			  btrfs_calc_delayed_ref_bytes(fs_info,
+					       BTRFS_UNLINK_METADATA_UNITS));
 
 	spin_lock(&sinfo->lock);
 	spin_lock(&block_rsv->lock);
diff --git a/fs/btrfs/block-rsv.h b/fs/btrfs/block-rsv.h
index df87c4949d06..fd8bfaf26da5 100644
--- a/fs/btrfs/block-rsv.h
+++ b/fs/btrfs/block-rsv.h
@@ -50,6 +50,18 @@ struct btrfs_block_rsv {
 	u64 qgroup_rsv_reserved;
 };
 
+/*
+ * Number of metadata items necessary for an unlink operation:
+ *
+ * 1 for the possible orphan item
+ * 1 for the dir item
+ * 1 for the dir index
+ * 1 for the inode ref
+ * 1 for the inode
+ * 1 for the parent inode
+ */
+#define BTRFS_UNLINK_METADATA_UNITS		6
+
 void btrfs_init_block_rsv(struct btrfs_block_rsv *rsv, enum btrfs_rsv_type type);
 void btrfs_init_root_block_rsv(struct btrfs_root *root);
 struct btrfs_block_rsv *btrfs_alloc_block_rsv(struct btrfs_fs_info *fs_info,
diff --git a/fs/btrfs/delayed-ref.h b/fs/btrfs/delayed-ref.h
index 712a6315e956..d325bf294867 100644
--- a/fs/btrfs/delayed-ref.h
+++ b/fs/btrfs/delayed-ref.h
@@ -253,6 +253,27 @@ extern struct kmem_cache *btrfs_delayed_extent_op_cachep;
 int __init btrfs_delayed_ref_init(void);
 void __cold btrfs_delayed_ref_exit(void);
 
+static inline u64 btrfs_calc_delayed_ref_bytes(struct btrfs_fs_info *fs_info,
+					       int num_delayed_refs)
+{
+	u64 num_bytes;
+
+	num_bytes = btrfs_calc_insert_metadata_size(fs_info, num_delayed_refs);
+
+	/*
+	 * We have to check the mount option here because we could be enabling
+	 * the free space tree for the first time and don't have the compat_ro
+	 * option set yet.
+	 *
+	 * We need extra reservations if we have the free space tree because
+	 * we'll have to modify that tree as well.
+	 */
+	if (btrfs_test_opt(fs_info, FREE_SPACE_TREE))
+		num_bytes *= 2;
+
+	return num_bytes;
+}
+
 static inline void btrfs_init_generic_ref(struct btrfs_ref *generic_ref,
 				int action, u64 bytenr, u64 len, u64 parent)
 {