diff --git a/src/sampler.jl b/src/sampler.jl
index cfc58942e..833aaf7e2 100644
--- a/src/sampler.jl
+++ b/src/sampler.jl
@@ -150,7 +150,7 @@ function set_values!!(
     flattened_param_vals = varinfo[spl]
     length(flattened_param_vals) == length(initial_params) || throw(
         DimensionMismatch(
-            "Provided initial value size ($(length(initial_params))) doesn't match the model size ($(length(theta)))",
+            "Provided initial value size ($(length(initial_params))) doesn't match the model size ($(length(flattened_param_vals)))",
         ),
     )
 
diff --git a/test/sampler.jl b/test/sampler.jl
index b29d3caf1..95e838167 100644
--- a/test/sampler.jl
+++ b/test/sampler.jl
@@ -162,6 +162,9 @@
             chain1 = sample(model, sampler, 1; progress=false)
             Random.seed!(1234)
             chain2 = sample(model, sampler, 1; initial_params=nothing, progress=false)
+            @test_throws DimensionMismatch sample(
+                model, sampler, 1; progress=false, initial_params=zeros(10)
+            )
             @test chain1[1].metadata.m.vals == chain2[1].metadata.m.vals
             @test chain1[1].metadata.s.vals == chain2[1].metadata.s.vals