diff --git a/dawg-ord.cabal b/dawg-ord.cabal
--- a/dawg-ord.cabal
+++ b/dawg-ord.cabal
@@ -1,5 +1,5 @@
 name:               dawg-ord
-version:            0.5.1.0
+version:            0.5.1.1
 synopsis:           Directed acyclic word graphs
 description:
     The library implements /directed acyclic word graphs/ (DAWGs) internally
@@ -29,7 +29,7 @@
     hs-source-dirs: src
     build-depends:
         base            >= 4        && < 5
-      , containers      >= 0.5      && < 0.6
+      , containers      >= 0.5      && < 0.7
       , vector          >= 0.10     && < 0.13
       , mtl             >= 2.1      && < 2.3
       , transformers    >= 0.3      && < 0.6
diff --git a/src/Data/DAWG/Gen/Graph.hs b/src/Data/DAWG/Gen/Graph.hs
--- a/src/Data/DAWG/Gen/Graph.hs
+++ b/src/Data/DAWG/Gen/Graph.hs
@@ -113,7 +113,7 @@
 
 -- | Increment the number of ingoing paths.
 incIngo :: ID -> Graph n -> Graph n
-incIngo i g = g { ingoMap = M.insertWith' (+) i 1 (ingoMap g) }
+incIngo i g = g { ingoMap = M.insertWith (+) i 1 (ingoMap g) }
 
 -- | Decrement the number of ingoing paths and return
 -- the resulting number.