diff --git a/Numeric/MCMC/Hamiltonian.hs b/Numeric/MCMC/Hamiltonian.hs
--- a/Numeric/MCMC/Hamiltonian.hs
+++ b/Numeric/MCMC/Hamiltonian.hs
@@ -126,7 +126,7 @@
   => Double -> Int -> Transition m (Chain (t Double) b)
 hamiltonian e l = do
   Chain {..} <- get
-  r0 <- lift (for chainPosition (const MWC.standard))
+  r0 <- lift (for chainPosition (const MWC.standardNormal))
   zc <- lift (MWC.uniform :: PrimMonad m => Prob m Double)
   let (q, r) = leapfrogIntegrator chainTarget e l (chainPosition, r0)
       perturbed      = nextState chainTarget (chainPosition, q) (r0, r) zc
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:             1.3.0
+version:             1.3.2
 synopsis:            Speedy traversal through parameter space.
 homepage:            http://github.com/jtobin/hasty-hamiltonian
 license:             MIT
@@ -53,7 +53,7 @@
       base             >= 4 && < 6
     , kan-extensions   >= 5 && < 6
     , mcmc-types       >= 1.0.1
-    , mwc-probability  >= 1.0.1
+    , mwc-probability  >= 2.0 && < 3
     , lens             >= 4 && < 5
     , pipes            >= 4 && < 5
     , primitive        >= 0.5 && < 1.0
@@ -69,6 +69,6 @@
   build-depends:
       ad                >= 4 && < 5
     , base              >= 4 && < 6
-    , mwc-probability   >= 1.0.1
+    , mwc-probability   >= 2.0 && < 3
     , hasty-hamiltonian