diff --git a/projects/miopen/src/kernels/miopen_cstdint.hpp b/projects/miopen/src/kernels/miopen_cstdint.hpp
index fa8d68f5fa58..ed4a4651bc93 100644
--- a/projects/miopen/src/kernels/miopen_cstdint.hpp
+++ b/projects/miopen/src/kernels/miopen_cstdint.hpp
@@ -33,8 +33,8 @@ typedef unsigned short uint16_t;
 #if HIP_PACKAGE_VERSION_FLAT >= 6000025000ULL
 typedef signed int int32_t;
 typedef unsigned int uint32_t;
-typedef __hip_internal::uint64_t uint64_t;
-typedef __hip_internal::int64_t int64_t;
+typedef __UINT64_TYPE__ uint64_t;
+typedef __INT64_TYPE__ int64_t;
 #endif
 
 #else
diff --git a/projects/miopen/test/gtest/miopen_cstdint_lp64.cpp b/projects/miopen/test/gtest/miopen_cstdint_lp64.cpp
new file mode 100644
index 000000000000..002263333ff8
--- /dev/null
+++ b/projects/miopen/test/gtest/miopen_cstdint_lp64.cpp
@@ -0,0 +1,58 @@
+// Copyright © Advanced Micro Devices, Inc., or its affiliates.
+// SPDX-License-Identifier:  MIT
+
+// Regression test for TheRock#6258 / LP64 typedef conflict in miopen_cstdint.hpp.
+//
+// On LP64 platforms (64-bit Linux, macOS), <stdint.h> defines uint64_t as
+// 'unsigned long', but __hip_internal::uint64_t is 'unsigned long long'.
+// These are distinct C++ types despite being the same width, so a typedef
+// redefinition is a hard error when both are visible during JIT compilation.
+//
+// This test exercises the real comgr JIT path via Handle::AddKernel with an
+// inline kernel that includes miopen_cstdint.hpp alongside system headers.
+
+#include <gtest/gtest.h>
+
+#include <miopen/handle.hpp>
+#include <miopen/manage_ptr.hpp>
+
+#include "get_handle.hpp"
+
+static std::string CstdintKernelSource()
+{
+    // Deliberately include <stdint.h> before miopen_cstdint.hpp to reproduce
+    // the original conflict: system uint64_t (unsigned long) vs the MIOpen
+    // typedef (previously unsigned long long via __hip_internal).
+    return "#ifndef MIOPEN_HIP_RUNTIME_COMPILE\n"
+           "#include <hip/hip_runtime.h>\n"
+           "#endif\n"
+           "#include <stdint.h>\n"
+           "#include \"miopen_cstdint.hpp\"\n"
+           "extern \"C\" {\n"
+           "__global__ void cstdint_write(uint64_t* data) {\n"
+           "    if(threadIdx.x == 0 && blockIdx.x == 0)\n"
+           "        data[0] = (uint64_t)42;\n"
+           "}\n"
+           "}\n";
+}
+
+TEST(CPU_MiopenCstdintLP64_NONE, JitCompileWithMiopenCstdint)
+{
+    auto&& h = get_handle();
+
+    std::vector<uint64_t> data_in(1, 0);
+    auto data_dev = h.Write(data_in);
+
+    h.AddKernel("NoAlgo",
+                "",
+                "cstdint_test.cpp",
+                "cstdint_write",
+                {1, 1, 1},
+                {1, 1, 1},
+                "",
+                0,
+                CstdintKernelSource())(data_dev.get());
+
+    auto data_out = h.Read<uint64_t>(data_dev, 1);
+    EXPECT_EQ(data_out[0], 42u);
+}