diff --git a/birch-beer.cabal b/birch-beer.cabal
--- a/birch-beer.cabal
+++ b/birch-beer.cabal
@@ -1,6 +1,6 @@
 cabal-version: >=1.10
 name: birch-beer
-version: 0.1.4.4
+version: 0.1.4.5
 license: GPL-3
 license-file: LICENSE
 copyright: 2019 Gregory W. Schwartz
diff --git a/src/BirchBeer/Types.hs b/src/BirchBeer/Types.hs
--- a/src/BirchBeer/Types.hs
+++ b/src/BirchBeer/Types.hs
@@ -31,6 +31,7 @@
 import qualified Data.Aeson.Types as A
 import qualified Data.Clustering.Hierarchical as HC
 import qualified Data.Graph.Inductive as G
+import qualified Data.Map.Strict as Map
 import qualified Data.Sequence as Seq
 import qualified Data.Set as Set
 import qualified Data.Sparse.Common as S
@@ -256,3 +257,9 @@
 
 instance (Semigroup a) => Monoid (TreeNode a) where
   mempty = TreeNode { _distance = Nothing, _item = mempty }
+
+instance Semigroup LabelMap where
+  (<>) (LabelMap x) (LabelMap y)  = LabelMap $ Map.union x y
+
+instance Monoid LabelMap where
+  mempty = LabelMap Map.empty