diff --git a/test/mcmc/hmc.jl b/test/mcmc/hmc.jl
index 6ac96a551..855d729e9 100644
--- a/test/mcmc/hmc.jl
+++ b/test/mcmc/hmc.jl
@@ -111,7 +111,7 @@ Enzyme.API.runtimeActivity!(true)
         alpha = 0.16                  # regularizatin term
         var_prior = sqrt(1.0 / alpha) # variance of the Gaussian prior
 
-        @model function bnn(ts)
+        @model function bnn(ts, var_prior)
             b1 ~ MvNormal([0. ;0.; 0.],
                 [var_prior 0. 0.; 0. var_prior 0.; 0. 0. var_prior])
             w11 ~ MvNormal([0.; 0.], [var_prior 0.; 0. var_prior])
@@ -129,7 +129,7 @@ Enzyme.API.runtimeActivity!(true)
         end
 
         # Sampling
-        chain = sample(rng, bnn(ts), HMC(0.1, 5; adtype=adbackend), 10)
+        chain = sample(rng, bnn(ts, var_prior), HMC(0.1, 5; adtype=adbackend), 10)
     end
 
     @testset "hmcda inference" begin