diff --git a/test/cuda_jamfile b/test/cuda_jamfile
index cd2fcc13..bac4ab2b 100644
--- a/test/cuda_jamfile
+++ b/test/cuda_jamfile
@@ -61,3 +61,6 @@ run test_signed_ge.cu ;
 
 run test_unsigned_cstdlib_div.cu ;
 run test_signed_cstdlib_div.cu ;
+
+run test_signed_to_unsigned_conversion.cu ;
+run test_unsigned_to_signed_conversion.cu ;
diff --git a/test/test_signed_to_unsigned_conversion.cu b/test/test_signed_to_unsigned_conversion.cu
new file mode 100644
index 00000000..5073f0f6
--- /dev/null
+++ b/test/test_signed_to_unsigned_conversion.cu
@@ -0,0 +1,110 @@
+//  Copyright Matt Borland 2026.
+//  Use, modification and distribution are subject to the
+//  Boost Software License, Version 1.0. (See accompanying file
+//  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#define BOOST_INT128_ALLOW_SIGN_CONVERSION
+
+#include <iostream>
+#include <iomanip>
+#include <vector>
+#include <random>
+#include <limits>
+#include <boost/int128.hpp>
+#include <boost/int128/random.hpp>
+#include <boost/random/uniform_int_distribution.hpp>
+#include "cuda_managed_ptr.hpp"
+#include "stopwatch.hpp"
+
+// For the CUDA runtime routines (prefixed with "cuda_")
+#include <cuda_runtime.h>
+
+using signed_type = boost::int128::int128_t;
+using unsigned_type = boost::int128::uint128_t;
+
+/**
+ * CUDA Kernel Device code
+ *
+ * Converts signed int128 values to unsigned int128 values
+ */
+__global__ void cuda_test(const signed_type *in, unsigned_type *out, int numElements)
+{
+    int i = blockDim.x * blockIdx.x + threadIdx.x;
+
+    if (i < numElements)
+    {
+        out[i] = unsigned_type(in[i]);
+    }
+}
+
+/**
+ * Host main routine
+ */
+int main(void)
+{
+    std::mt19937_64 rng {42};
+
+    // Error code to check return values for CUDA calls
+    cudaError_t err = cudaSuccess;
+
+    // Print the vector length to be used, and compute its size
+    int numElements = 50000;
+    std::cout << "[Vector operation on " << numElements << " elements]" << std::endl;
+
+    // Allocate the managed input vector
+    cuda_managed_ptr<signed_type> input_vector(numElements);
+
+    // Allocate the managed output vector
+    cuda_managed_ptr<unsigned_type> output_vector(numElements);
+
+    // Initialize the input vectors with non-negative values so bit patterns match
+    boost::random::uniform_int_distribution<signed_type> dist {signed_type{0}, (std::numeric_limits<signed_type>::max)()};
+    for (std::size_t i = 0; i < numElements; ++i)
+    {
+        input_vector[i] = dist(rng);
+    }
+
+    // Launch the CUDA Kernel
+    int threadsPerBlock = 256;
+    int blocksPerGrid =(numElements + threadsPerBlock - 1) / threadsPerBlock;
+    std::cout << "CUDA kernel launch with " << blocksPerGrid << " blocks of " << threadsPerBlock << " threads" << std::endl;
+
+    watch w;
+
+    cuda_test<<<blocksPerGrid, threadsPerBlock>>>(input_vector.get(), output_vector.get(), numElements);
+    cudaDeviceSynchronize();
+
+    std::cout << "CUDA kernal done in: " << w.elapsed() << "s" << std::endl;
+
+    err = cudaGetLastError();
+
+    if (err != cudaSuccess)
+    {
+        std::cerr << "Failed to launch kernel (error code " << cudaGetErrorString(err) << ")!" << std::endl;
+        return EXIT_FAILURE;
+    }
+
+    // Verify that the result vector is correct
+    std::vector<unsigned_type> results;
+    results.reserve(numElements);
+    w.reset();
+    for(int i = 0; i < numElements; ++i)
+    {
+        results.push_back(unsigned_type(input_vector[i]));
+    }
+    double t = w.elapsed();
+    // check the results
+    for(int i = 0; i < numElements; ++i)
+    {
+        if (output_vector[i] != results[i])
+        {
+            std::cerr << "Result verification failed at element " << i << "!" << std::endl;
+            return EXIT_FAILURE;
+        }
+    }
+
+    std::cout << "Test PASSED, normal calculation time: " << t << "s" << std::endl;
+    std::cout << "Done\n";
+
+    return 0;
+}
diff --git a/test/test_unsigned_to_signed_conversion.cu b/test/test_unsigned_to_signed_conversion.cu
new file mode 100644
index 00000000..016e7a5d
--- /dev/null
+++ b/test/test_unsigned_to_signed_conversion.cu
@@ -0,0 +1,110 @@
+//  Copyright Matt Borland 2026.
+//  Use, modification and distribution are subject to the
+//  Boost Software License, Version 1.0. (See accompanying file
+//  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#define BOOST_INT128_ALLOW_SIGN_CONVERSION
+
+#include <iostream>
+#include <iomanip>
+#include <vector>
+#include <random>
+#include <limits>
+#include <boost/int128.hpp>
+#include <boost/int128/random.hpp>
+#include <boost/random/uniform_int_distribution.hpp>
+#include "cuda_managed_ptr.hpp"
+#include "stopwatch.hpp"
+
+// For the CUDA runtime routines (prefixed with "cuda_")
+#include <cuda_runtime.h>
+
+using signed_type = boost::int128::int128_t;
+using unsigned_type = boost::int128::uint128_t;
+
+/**
+ * CUDA Kernel Device code
+ *
+ * Converts unsigned int128 values to signed int128 values
+ */
+__global__ void cuda_test(const unsigned_type *in, signed_type *out, int numElements)
+{
+    int i = blockDim.x * blockIdx.x + threadIdx.x;
+
+    if (i < numElements)
+    {
+        out[i] = signed_type(in[i]);
+    }
+}
+
+/**
+ * Host main routine
+ */
+int main(void)
+{
+    std::mt19937_64 rng {42};
+
+    // Error code to check return values for CUDA calls
+    cudaError_t err = cudaSuccess;
+
+    // Print the vector length to be used, and compute its size
+    int numElements = 50000;
+    std::cout << "[Vector operation on " << numElements << " elements]" << std::endl;
+
+    // Allocate the managed input vector
+    cuda_managed_ptr<unsigned_type> input_vector(numElements);
+
+    // Allocate the managed output vector
+    cuda_managed_ptr<signed_type> output_vector(numElements);
+
+    // Initialize the input vectors with values that fit in signed range
+    boost::random::uniform_int_distribution<unsigned_type> dist {unsigned_type{0U}, static_cast<unsigned_type>((std::numeric_limits<signed_type>::max)())};
+    for (std::size_t i = 0; i < numElements; ++i)
+    {
+        input_vector[i] = dist(rng);
+    }
+
+    // Launch the CUDA Kernel
+    int threadsPerBlock = 256;
+    int blocksPerGrid =(numElements + threadsPerBlock - 1) / threadsPerBlock;
+    std::cout << "CUDA kernel launch with " << blocksPerGrid << " blocks of " << threadsPerBlock << " threads" << std::endl;
+
+    watch w;
+
+    cuda_test<<<blocksPerGrid, threadsPerBlock>>>(input_vector.get(), output_vector.get(), numElements);
+    cudaDeviceSynchronize();
+
+    std::cout << "CUDA kernal done in: " << w.elapsed() << "s" << std::endl;
+
+    err = cudaGetLastError();
+
+    if (err != cudaSuccess)
+    {
+        std::cerr << "Failed to launch kernel (error code " << cudaGetErrorString(err) << ")!" << std::endl;
+        return EXIT_FAILURE;
+    }
+
+    // Verify that the result vector is correct
+    std::vector<signed_type> results;
+    results.reserve(numElements);
+    w.reset();
+    for(int i = 0; i < numElements; ++i)
+    {
+        results.push_back(signed_type(input_vector[i]));
+    }
+    double t = w.elapsed();
+    // check the results
+    for(int i = 0; i < numElements; ++i)
+    {
+        if (output_vector[i] != results[i])
+        {
+            std::cerr << "Result verification failed at element " << i << "!" << std::endl;
+            return EXIT_FAILURE;
+        }
+    }
+
+    std::cout << "Test PASSED, normal calculation time: " << t << "s" << std::endl;
+    std::cout << "Done\n";
+
+    return 0;
+}