diff --git a/test/sample.jl b/test/sample.jl
index 00f7ccae..b07387c7 100644
--- a/test/sample.jl
+++ b/test/sample.jl
@@ -292,11 +292,16 @@
     
     @testset "Testing callbacks" begin
         function count_iterations(rng, model, sampler, sample, state, i; iter_array, kwargs...)
-            iter_array[i] = i
+            push!(iter_array, i)
         end
         N = 100
-        it_array = zeros(N)
+        it_array = Float64[]
         sample(MyModel(), MySampler(), N; callback=count_iterations, iter_array=it_array)
         @test it_array == collect(1:N)
+
+        # sampling without predetermined N
+        it_array = Float64[]
+        chain = sample(MyModel(), MySampler(); callback=count_iterations, iter_array=it_array)
+        @test it_array == collect(1:size(chain, 1))
     end
 end