diff --git a/src/C_API.jl b/src/C_API.jl
index 6f985ef..5028aaa 100644
--- a/src/C_API.jl
+++ b/src/C_API.jl
@@ -1455,7 +1455,7 @@ function t4a_simplett_c64_site_tensor(
         ptr,
         Csize_t(site),
         out_data,
-        Csize_t(length(out_data) ÷ 2),
+        Csize_t(length(out_data)),
         out_left_dim,
         out_site_dim,
         out_right_dim
diff --git a/test/test_conversions.jl b/test/test_conversions.jl
new file mode 100644
index 0000000..fff7205
--- /dev/null
+++ b/test/test_conversions.jl
@@ -0,0 +1,105 @@
+using Test
+using Tensor4all
+using Tensor4all.SimpleTT
+using Tensor4all.TreeTN
+
+import Tensor4all.SimpleTT: sitedims, linkdims, evaluate, sitetensor, fulltensor
+import Tensor4all.TreeTN: MPS, nv, inner, linkdims as ttn_linkdims
+using LinearAlgebra: norm
+
+@testset "SimpleTT <-> TreeTN Conversions" begin
+    @testset "SimpleTT -> MPS -> SimpleTT round-trip" begin
+        @testset "rank-1 constant" begin
+            tt = SimpleTensorTrain([2, 3, 4], 1.5)
+            mps = MPS(tt)
+            @test nv(mps) == 3
+
+            tt2 = SimpleTensorTrain(mps)
+            @test length(tt2) == 3
+            @test sitedims(tt2) == [2, 3, 4]
+
+            # Check values match
+            arr1 = fulltensor(tt)
+            arr2 = fulltensor(tt2)
+            @test arr1 ≈ arr2
+        end
+
+        @testset "higher rank" begin
+            t1 = randn(1, 2, 3)
+            t2 = randn(3, 4, 2)
+            t3 = randn(2, 3, 1)
+            tt = SimpleTensorTrain([t1, t2, t3])
+            mps = MPS(tt)
+            @test nv(mps) == 3
+
+            tt2 = SimpleTensorTrain(mps)
+            @test length(tt2) == 3
+            @test sitedims(tt2) == [2, 4, 3]
+            @test linkdims(tt2) == [3, 2]
+
+            arr1 = fulltensor(tt)
+            arr2 = fulltensor(tt2)
+            @test arr1 ≈ arr2
+        end
+
+        @testset "single site" begin
+            tt = SimpleTensorTrain([3], 2.0)
+            mps = MPS(tt)
+            @test nv(mps) == 1
+
+            tt2 = SimpleTensorTrain(mps)
+            @test length(tt2) == 1
+            @test sitedims(tt2) == [3]
+
+            arr1 = fulltensor(tt)
+            arr2 = fulltensor(tt2)
+            @test arr1 ≈ arr2
+        end
+
+        @testset "two sites" begin
+            tt = SimpleTensorTrain([2, 5], 3.0)
+            mps = MPS(tt)
+            @test nv(mps) == 2
+
+            tt2 = SimpleTensorTrain(mps)
+            @test length(tt2) == 2
+            @test sitedims(tt2) == [2, 5]
+
+            arr1 = fulltensor(tt)
+            arr2 = fulltensor(tt2)
+            @test arr1 ≈ arr2
+        end
+    end
+
+    @testset "ComplexF64 round-trip" begin
+        tt = SimpleTensorTrain([2, 3, 4], 1.0 + 2.0im)
+        mps = MPS(tt)
+        @test nv(mps) == 3
+
+        tt2 = SimpleTensorTrain(mps)
+        @test length(tt2) == 3
+        @test sitedims(tt2) == [2, 3, 4]
+
+        arr1 = fulltensor(tt)
+        arr2 = fulltensor(tt2)
+        @test arr1 ≈ arr2
+    end
+
+    @testset "MPS -> SimpleTT -> MPS" begin
+        sites = [Tensor4all.Index(2) for _ in 1:4]
+        mps = TreeTN.random_mps(sites; linkdims=3)
+
+        tt = SimpleTensorTrain(mps)
+        @test length(tt) == 4
+        @test sitedims(tt) == [2, 2, 2, 2]
+
+        mps2 = MPS(tt)
+        @test nv(mps2) == 4
+
+        # Check that the dense tensor representation matches
+        dense1 = TreeTN.to_dense(mps)
+        arr1 = data(dense1)
+        arr2 = fulltensor(tt)
+        @test arr1 ≈ arr2
+    end
+end