diff --git a/Numeric/MCMC/Hamiltonian.hs b/Numeric/MCMC/Hamiltonian.hs
--- a/Numeric/MCMC/Hamiltonian.hs
+++ b/Numeric/MCMC/Hamiltonian.hs
@@ -153,7 +153,7 @@
 
 -- The leapfrog or Stormer-Verlet integrator.
 leapfrogIntegrator
-  :: (Num (IxValue (f Double)), Num (IxValue (t Double))
+  :: (Num (IxValue (f Double))
      , FunctorWithIndex (Index (f Double)) t
      , FunctorWithIndex (Index (t Double)) f
      , Ixed (f Double), Ixed (t Double)
@@ -171,7 +171,7 @@
 
 -- A single leapfrog step.
 leapfrog
-  :: (Num (IxValue (f Double)), Num (IxValue (t Double))
+  :: (Num (IxValue (f Double))
      , FunctorWithIndex (Index (f Double)) t
      , FunctorWithIndex (Index (t Double)) f
      , Ixed (t Double), Ixed (f Double)
diff --git a/hasty-hamiltonian.cabal b/hasty-hamiltonian.cabal
--- a/hasty-hamiltonian.cabal
+++ b/hasty-hamiltonian.cabal
@@ -1,5 +1,5 @@
 name:                hasty-hamiltonian
-version:             1.1.3
+version:             1.1.4
 synopsis:            Speedy traversal through parameter space.
 homepage:            http://github.com/jtobin/hasty-hamiltonian
 license:             MIT
@@ -49,7 +49,7 @@
   exposed-modules:
     Numeric.MCMC.Hamiltonian
   build-depends:
-      base             <  5
+      base             >= 4 && < 6
     , mcmc-types       >= 1.0.1
     , mwc-probability  >= 1.0.1
     , lens             >= 4 && < 5
@@ -66,7 +66,7 @@
     -rtsopts
   build-depends:
       ad                >= 4 && < 5
-    , base              < 5
+    , base              >= 4 && < 6
     , mwc-probability   >= 1.0.1
     , hasty-hamiltonian