diff --git a/Data/Graph/Dom.hs b/Data/Graph/Dom.hs
--- a/Data/Graph/Dom.hs
+++ b/Data/Graph/Dom.hs
@@ -242,7 +242,6 @@
   lw  <- labelM w
   zw  <- sizeM w
   store labelE s lw
-  sv <- sizeM v
   store sizeE v . (+zw) =<< sizeM v
   let follow s = do
         when (s /= n0) (do
diff --git a/dom-lt.cabal b/dom-lt.cabal
--- a/dom-lt.cabal
+++ b/dom-lt.cabal
@@ -1,5 +1,5 @@
 name:               dom-lt
-version:            0.1.2
+version:            0.1.3
 cabal-version:      >= 1.6
 build-type:         Simple
 license:            BSD3
@@ -17,7 +17,7 @@
   build-tools:
   extra-libraries:
   hs-source-dirs:   .
-  ghc-options:      -O2
+  ghc-options:      -O2 -funbox-strict-fields
   extensions:       RankNTypes
   build-depends:    base==4.*, array, containers
   exposed-modules:  Data.Graph.Dom