diff --git a/.gitignore b/.gitignore
index e9aaa394..a8f98d4c 100644
--- a/.gitignore
+++ b/.gitignore
@@ -397,7 +397,7 @@ __pycache__/
 # run git update-index --assume-unchanged lib/zlib/zconf.h
 lib/zlib
 # Files generated by CMake
-src/inc/MSIXResource.hpp
+src/inc/internal/MSIXResource.hpp
 src/msix/MSIXResource.cpp
 src/msix/common/MSIXResource.cpp
 
diff --git a/cmake/msix_resources.cmake b/cmake/msix_resources.cmake
index 24e473a2..08f29077 100644
--- a/cmake/msix_resources.cmake
+++ b/cmake/msix_resources.cmake
@@ -348,5 +348,5 @@ foreach(FILE ${RESOURCES_CERTS})
     string(APPEND CERTS_HPP result.push_back(std::make_pair(\"${FILE}\", std::move(factory->GetResource(\"${FILE}\")))) ";\n\t\t\t\t")
 endforeach()
 
-configure_file(${MSIX_PROJECT_ROOT}/src/inc/MSIXResource.hpp.cmakein ${MSIX_PROJECT_ROOT}/src/inc/MSIXResource.hpp CRLF)
+configure_file(${MSIX_PROJECT_ROOT}/src/inc/internal/MSIXResource.hpp.cmakein ${MSIX_PROJECT_ROOT}/src/inc/internal/MSIXResource.hpp CRLF)
 configure_file(${MSIX_PROJECT_ROOT}/src/msix/common/MSIXResource.cpp.cmakein ${MSIX_PROJECT_ROOT}/src/msix/common/MSIXResource.cpp CRLF)
diff --git a/pipelines/azure-pipelines-windows.yml b/pipelines/azure-pipelines-windows.yml
index 78557298..04c60c3d 100644
--- a/pipelines/azure-pipelines-windows.yml
+++ b/pipelines/azure-pipelines-windows.yml
@@ -73,8 +73,8 @@ jobs:
         _arguments: x86 -d --pack
         _artifact: WIN32chk-pack
       debug_64_pack:
-        _arguments: x86 -d --pack
-        _artifact: WIN32chk-pack
+        _arguments: x64 -d --pack
+        _artifact: WIN32-x64chk-pack
 
   steps:
   - task: BatchScript@1
diff --git a/src/inc/Applicability.hpp b/src/inc/internal/Applicability.hpp
similarity index 100%
rename from src/inc/Applicability.hpp
rename to src/inc/internal/Applicability.hpp
diff --git a/src/inc/AppxBlockMapObject.hpp b/src/inc/internal/AppxBlockMapObject.hpp
similarity index 100%
rename from src/inc/AppxBlockMapObject.hpp
rename to src/inc/internal/AppxBlockMapObject.hpp
diff --git a/src/inc/AppxBlockMapWriter.hpp b/src/inc/internal/AppxBlockMapWriter.hpp
similarity index 100%
rename from src/inc/AppxBlockMapWriter.hpp
rename to src/inc/internal/AppxBlockMapWriter.hpp
diff --git a/src/inc/AppxBundleManifest.hpp b/src/inc/internal/AppxBundleManifest.hpp
similarity index 100%
rename from src/inc/AppxBundleManifest.hpp
rename to src/inc/internal/AppxBundleManifest.hpp
diff --git a/src/inc/AppxFactory.hpp b/src/inc/internal/AppxFactory.hpp
similarity index 100%
rename from src/inc/AppxFactory.hpp
rename to src/inc/internal/AppxFactory.hpp
diff --git a/src/inc/AppxFile.hpp b/src/inc/internal/AppxFile.hpp
similarity index 100%
rename from src/inc/AppxFile.hpp
rename to src/inc/internal/AppxFile.hpp
diff --git a/src/inc/AppxManifestObject.hpp b/src/inc/internal/AppxManifestObject.hpp
similarity index 100%
rename from src/inc/AppxManifestObject.hpp
rename to src/inc/internal/AppxManifestObject.hpp
diff --git a/src/inc/AppxManifestValidation.hpp b/src/inc/internal/AppxManifestValidation.hpp
similarity index 100%
rename from src/inc/AppxManifestValidation.hpp
rename to src/inc/internal/AppxManifestValidation.hpp
diff --git a/src/inc/AppxPackageInfo.hpp b/src/inc/internal/AppxPackageInfo.hpp
similarity index 100%
rename from src/inc/AppxPackageInfo.hpp
rename to src/inc/internal/AppxPackageInfo.hpp
diff --git a/src/inc/AppxPackageObject.hpp b/src/inc/internal/AppxPackageObject.hpp
similarity index 100%
rename from src/inc/AppxPackageObject.hpp
rename to src/inc/internal/AppxPackageObject.hpp
diff --git a/src/inc/AppxPackageWriter.hpp b/src/inc/internal/AppxPackageWriter.hpp
similarity index 100%
rename from src/inc/AppxPackageWriter.hpp
rename to src/inc/internal/AppxPackageWriter.hpp
diff --git a/src/inc/AppxSignature.hpp b/src/inc/internal/AppxSignature.hpp
similarity index 100%
rename from src/inc/AppxSignature.hpp
rename to src/inc/internal/AppxSignature.hpp
diff --git a/src/inc/BlockMapStream.hpp b/src/inc/internal/BlockMapStream.hpp
similarity index 100%
rename from src/inc/BlockMapStream.hpp
rename to src/inc/internal/BlockMapStream.hpp
diff --git a/src/inc/ContentType.hpp b/src/inc/internal/ContentType.hpp
similarity index 100%
rename from src/inc/ContentType.hpp
rename to src/inc/internal/ContentType.hpp
diff --git a/src/inc/ContentTypeWriter.hpp b/src/inc/internal/ContentTypeWriter.hpp
similarity index 100%
rename from src/inc/ContentTypeWriter.hpp
rename to src/inc/internal/ContentTypeWriter.hpp
diff --git a/src/inc/Crypto.hpp b/src/inc/internal/Crypto.hpp
similarity index 100%
rename from src/inc/Crypto.hpp
rename to src/inc/internal/Crypto.hpp
diff --git a/src/inc/DeflateStream.hpp b/src/inc/internal/DeflateStream.hpp
similarity index 100%
rename from src/inc/DeflateStream.hpp
rename to src/inc/internal/DeflateStream.hpp
diff --git a/src/inc/DirectoryObject.hpp b/src/inc/internal/DirectoryObject.hpp
similarity index 100%
rename from src/inc/DirectoryObject.hpp
rename to src/inc/internal/DirectoryObject.hpp
diff --git a/src/inc/Encoding.hpp b/src/inc/internal/Encoding.hpp
similarity index 100%
rename from src/inc/Encoding.hpp
rename to src/inc/internal/Encoding.hpp
diff --git a/src/inc/Enumerators.hpp b/src/inc/internal/Enumerators.hpp
similarity index 100%
rename from src/inc/Enumerators.hpp
rename to src/inc/internal/Enumerators.hpp
diff --git a/src/inc/FileNameValidation.hpp b/src/inc/internal/FileNameValidation.hpp
similarity index 100%
rename from src/inc/FileNameValidation.hpp
rename to src/inc/internal/FileNameValidation.hpp
diff --git a/src/inc/FileStream.hpp b/src/inc/internal/FileStream.hpp
similarity index 100%
rename from src/inc/FileStream.hpp
rename to src/inc/internal/FileStream.hpp
diff --git a/src/inc/HashStream.hpp b/src/inc/internal/HashStream.hpp
similarity index 100%
rename from src/inc/HashStream.hpp
rename to src/inc/internal/HashStream.hpp
diff --git a/src/inc/ICompressionObject.hpp b/src/inc/internal/ICompressionObject.hpp
similarity index 100%
rename from src/inc/ICompressionObject.hpp
rename to src/inc/internal/ICompressionObject.hpp
diff --git a/src/inc/IXml.hpp b/src/inc/internal/IXml.hpp
similarity index 81%
rename from src/inc/IXml.hpp
rename to src/inc/internal/IXml.hpp
index c74541e1..49504e5c 100644
--- a/src/inc/IXml.hpp
+++ b/src/inc/internal/IXml.hpp
@@ -194,13 +194,58 @@ MSIX_INTERFACE(IXmlFactory, 0xf82a60ec,0xfbfc,0x4cb9,0xbc,0x04,0x1a,0x0f,0xe2,0x
 namespace MSIX {
     MSIX::ComPtr<IXmlFactory> CreateXmlFactory(IMsixFactory* factory);
 
+    template <typename T>
+    struct StringToNumber
+    {
+        static uint32_t Get(const std::string&)
+        {
+            static_assert(False<T>::value, "An appropriate specialization must be specified");
+        }
+    };
+
+    template <>
+    struct StringToNumber<std::uint32_t>
+    {
+        static uint32_t Get(const std::string& str)
+        {
+            return static_cast<uint32_t>(std::stoul(str));
+        }
+    };
+
+    template <>
+    struct StringToNumber<std::uint64_t>
+    {
+        static uint64_t Get(const std::string& str)
+        {
+            return static_cast<uint64_t>(std::stoull(str));
+        }
+    };
+
     template <class T>
     static T GetNumber(const ComPtr<IXmlElement>& element, XmlAttributeName attribute, T defaultValue)
     {
         const auto& attributeValue = element->GetAttributeValue(attribute);
         bool hasValue = !attributeValue.empty();
         T value = defaultValue;
-        if (hasValue) { value = static_cast<T>(std::stoul(attributeValue)); }
+        if (hasValue)
+        {
+            try
+            {
+                value = StringToNumber<T>::Get(attributeValue);
+            }
+            catch (std::invalid_argument& ia)
+            {
+                ThrowErrorAndLog(Error::XmlInvalidData, ia.what());
+            }
+            catch (std::out_of_range& oor)
+            {
+                ThrowErrorAndLog(Error::XmlInvalidData, oor.what());
+            }
+            catch (...)
+            {
+                ThrowErrorAndLog(Error::XmlInvalidData, "Unexpected exception converting string to number");
+            }
+        }
         return value;
     }
 
diff --git a/src/inc/InflateStream.hpp b/src/inc/internal/InflateStream.hpp
similarity index 100%
rename from src/inc/InflateStream.hpp
rename to src/inc/internal/InflateStream.hpp
diff --git a/src/inc/Log.hpp b/src/inc/internal/Log.hpp
similarity index 100%
rename from src/inc/Log.hpp
rename to src/inc/internal/Log.hpp
diff --git a/src/inc/MSIXFactory.hpp b/src/inc/internal/MSIXFactory.hpp
similarity index 100%
rename from src/inc/MSIXFactory.hpp
rename to src/inc/internal/MSIXFactory.hpp
diff --git a/src/inc/MSIXResource.hpp.cmakein b/src/inc/internal/MSIXResource.hpp.cmakein
similarity index 100%
rename from src/inc/MSIXResource.hpp.cmakein
rename to src/inc/internal/MSIXResource.hpp.cmakein
diff --git a/src/inc/MsixFeatureSelector.hpp b/src/inc/internal/MsixFeatureSelector.hpp
similarity index 100%
rename from src/inc/MsixFeatureSelector.hpp
rename to src/inc/internal/MsixFeatureSelector.hpp
diff --git a/src/inc/ObjectBase.hpp b/src/inc/internal/ObjectBase.hpp
similarity index 100%
rename from src/inc/ObjectBase.hpp
rename to src/inc/internal/ObjectBase.hpp
diff --git a/src/inc/internal/README.txt b/src/inc/internal/README.txt
new file mode 100644
index 00000000..0774b6a2
--- /dev/null
+++ b/src/inc/internal/README.txt
@@ -0,0 +1 @@
+Contains headers for consumption by both the product and *unit* tests.
\ No newline at end of file
diff --git a/src/inc/RangeStream.hpp b/src/inc/internal/RangeStream.hpp
similarity index 100%
rename from src/inc/RangeStream.hpp
rename to src/inc/internal/RangeStream.hpp
diff --git a/src/inc/ScopeExit.hpp b/src/inc/internal/ScopeExit.hpp
similarity index 100%
rename from src/inc/ScopeExit.hpp
rename to src/inc/internal/ScopeExit.hpp
diff --git a/src/inc/SignatureValidator.hpp b/src/inc/internal/SignatureValidator.hpp
similarity index 100%
rename from src/inc/SignatureValidator.hpp
rename to src/inc/internal/SignatureValidator.hpp
diff --git a/src/inc/StorageObject.hpp b/src/inc/internal/StorageObject.hpp
similarity index 100%
rename from src/inc/StorageObject.hpp
rename to src/inc/internal/StorageObject.hpp
diff --git a/src/inc/StreamHelper.hpp b/src/inc/internal/StreamHelper.hpp
similarity index 100%
rename from src/inc/StreamHelper.hpp
rename to src/inc/internal/StreamHelper.hpp
diff --git a/src/inc/StringHelper.hpp b/src/inc/internal/StringHelper.hpp
similarity index 100%
rename from src/inc/StringHelper.hpp
rename to src/inc/internal/StringHelper.hpp
diff --git a/src/inc/StringStream.hpp b/src/inc/internal/StringStream.hpp
similarity index 100%
rename from src/inc/StringStream.hpp
rename to src/inc/internal/StringStream.hpp
diff --git a/src/inc/UnicodeConversion.hpp b/src/inc/internal/UnicodeConversion.hpp
similarity index 100%
rename from src/inc/UnicodeConversion.hpp
rename to src/inc/internal/UnicodeConversion.hpp
diff --git a/src/inc/VectorStream.hpp b/src/inc/internal/VectorStream.hpp
similarity index 100%
rename from src/inc/VectorStream.hpp
rename to src/inc/internal/VectorStream.hpp
diff --git a/src/inc/VerifierObject.hpp b/src/inc/internal/VerifierObject.hpp
similarity index 100%
rename from src/inc/VerifierObject.hpp
rename to src/inc/internal/VerifierObject.hpp
diff --git a/src/inc/XmlWriter.hpp b/src/inc/internal/XmlWriter.hpp
similarity index 100%
rename from src/inc/XmlWriter.hpp
rename to src/inc/internal/XmlWriter.hpp
diff --git a/src/inc/ZipFileStream.hpp b/src/inc/internal/ZipFileStream.hpp
similarity index 100%
rename from src/inc/ZipFileStream.hpp
rename to src/inc/internal/ZipFileStream.hpp
diff --git a/src/inc/ZipObject.hpp b/src/inc/internal/ZipObject.hpp
similarity index 100%
rename from src/inc/ZipObject.hpp
rename to src/inc/internal/ZipObject.hpp
diff --git a/src/inc/ZipObjectReader.hpp b/src/inc/internal/ZipObjectReader.hpp
similarity index 100%
rename from src/inc/ZipObjectReader.hpp
rename to src/inc/internal/ZipObjectReader.hpp
diff --git a/src/inc/ZipObjectWriter.hpp b/src/inc/internal/ZipObjectWriter.hpp
similarity index 100%
rename from src/inc/ZipObjectWriter.hpp
rename to src/inc/internal/ZipObjectWriter.hpp
diff --git a/src/inc/AppxPackaging.hpp b/src/inc/public/AppxPackaging.hpp
similarity index 100%
rename from src/inc/AppxPackaging.hpp
rename to src/inc/public/AppxPackaging.hpp
diff --git a/src/inc/MSIXWindows.hpp b/src/inc/public/MSIXWindows.hpp
similarity index 100%
rename from src/inc/MSIXWindows.hpp
rename to src/inc/public/MSIXWindows.hpp
diff --git a/src/inc/MsixErrors.hpp b/src/inc/public/MsixErrors.hpp
similarity index 94%
rename from src/inc/MsixErrors.hpp
rename to src/inc/public/MsixErrors.hpp
index 7223f75f..59902444 100644
--- a/src/inc/MsixErrors.hpp
+++ b/src/inc/public/MsixErrors.hpp
@@ -3,6 +3,8 @@
 //  See LICENSE file in the project root for full license information.
 // 
 #pragma once
+#ifndef MSIX_MSIX_ERRORS__H
+#define MSIX_MSIX_ERRORS__H
 
 namespace MSIX {
 
@@ -84,5 +86,8 @@ namespace MSIX {
         XmlWarning                  = XML_FACILITY + 0x0001,
         XmlError                    = XML_FACILITY + 0x0002,
         XmlFatal                    = XML_FACILITY + 0x0003,
+        XmlInvalidData              = XML_FACILITY + 0x0004,
     };
 }
+
+#endif
diff --git a/src/inc/public/README.txt b/src/inc/public/README.txt
new file mode 100644
index 00000000..0c93c174
--- /dev/null
+++ b/src/inc/public/README.txt
@@ -0,0 +1 @@
+Contains headers for public consumption; can only reference each other and external dependencies.
\ No newline at end of file
diff --git a/src/inc/ComHelper.hpp b/src/inc/shared/ComHelper.hpp
similarity index 100%
rename from src/inc/ComHelper.hpp
rename to src/inc/shared/ComHelper.hpp
diff --git a/src/inc/Exceptions.hpp b/src/inc/shared/Exceptions.hpp
similarity index 94%
rename from src/inc/Exceptions.hpp
rename to src/inc/shared/Exceptions.hpp
index 1b48d4d1..0888006d 100644
--- a/src/inc/Exceptions.hpp
+++ b/src/inc/shared/Exceptions.hpp
@@ -11,10 +11,21 @@
 #include <functional>
 #include <sstream>
 
-#include "Log.hpp"
 #include "MSIXWindows.hpp"
 #include "MsixErrors.hpp"
 
+#ifndef MSIX_TEST
+#include "Log.hpp"
+#else
+namespace MSIX {
+    namespace Global {
+        namespace Log {
+            inline void Append(const std::string&) {}
+        }
+    }
+}
+#endif
+
 namespace MSIX {
 
     // Defines a common exception type to throw in exceptional cases.  DO NOT USE FOR FLOW CONTROL!
@@ -122,7 +133,11 @@ namespace MSIX {
 #define ThrowErrorIf(c, a, m) ThrowErrorIfNot(c,!(a), m)
 #define ThrowErrorAndLog(c, m) { MSIX::RaiseException<MSIX::Exception>(__LINE__, __FILE__, m, c); }
 
+#ifndef MSIX_TEST
 #define ThrowHrIfFailed(a) MSIX::RaiseExceptionIfFailed(a, __LINE__, __FILE__);
+#else
+#define ThrowHrIfFailed(a) { HRESULT __excMacroHR = (a); ThrowErrorIf(__excMacroHR, FAILED(__excMacroHR), nullptr) }
+#endif
 
 #ifdef WIN32
     #define ThrowHrIfFalse(a, m)                                                                               \
diff --git a/src/inc/shared/README.txt b/src/inc/shared/README.txt
new file mode 100644
index 00000000..32c0b337
--- /dev/null
+++ b/src/inc/shared/README.txt
@@ -0,0 +1,3 @@
+Contains headers for consumption by both the product and *functional* tests; can only reference each other, public headers, and external dependencies.
+
+Any functions used by tests must be implemented in the headers, as the tests will not be linking in anything.
\ No newline at end of file
diff --git a/src/inc/StreamBase.hpp b/src/inc/shared/StreamBase.hpp
similarity index 100%
rename from src/inc/StreamBase.hpp
rename to src/inc/shared/StreamBase.hpp
diff --git a/src/msix/CMakeLists.txt b/src/msix/CMakeLists.txt
index 75d3afdf..f82dbad8 100644
--- a/src/msix/CMakeLists.txt
+++ b/src/msix/CMakeLists.txt
@@ -87,9 +87,9 @@ endif()
 include(msix_resources) # Handles all the certificates and schemas we are going to use.
 
 set(LIB_PUBLIC_HEADERS
-    ../inc/AppxPackaging.hpp
-    ../inc/MSIXWindows.hpp
-    ../inc/MsixErrors.hpp
+    ../inc/public/AppxPackaging.hpp
+    ../inc/public/MSIXWindows.hpp
+    ../inc/public/MsixErrors.hpp
 )
 
 set(MsixSrc) # list with all the files we are going to use
@@ -230,13 +230,13 @@ add_library(${PROJECT_NAME} SHARED
 add_dependencies(${PROJECT_NAME} LIBS)
 
 # Copy out public headers to <binary dir>/src/unpack
-configure_file(../inc/MSIXWindows.hpp   ${CMAKE_CURRENT_BINARY_DIR}/MSIXWindows.hpp  )
-configure_file(../inc/AppxPackaging.hpp ${CMAKE_CURRENT_BINARY_DIR}/AppxPackaging.hpp)
-configure_file(../inc/MsixErrors.hpp ${CMAKE_CURRENT_BINARY_DIR}/MsixErrors.hpp)
+configure_file(../inc/public/MSIXWindows.hpp   ${CMAKE_CURRENT_BINARY_DIR}/MSIXWindows.hpp  )
+configure_file(../inc/public/AppxPackaging.hpp ${CMAKE_CURRENT_BINARY_DIR}/AppxPackaging.hpp)
+configure_file(../inc/public/MsixErrors.hpp    ${CMAKE_CURRENT_BINARY_DIR}/MsixErrors.hpp)
 
 # Linker and includes
 # Include MSIX headers
-target_include_directories(${PROJECT_NAME} PRIVATE ${MSIX_PROJECT_ROOT}/src/inc)
+target_include_directories(${PROJECT_NAME} PRIVATE ${MSIX_PROJECT_ROOT}/src/inc/public ${MSIX_PROJECT_ROOT}/src/inc/shared ${MSIX_PROJECT_ROOT}/src/inc/internal)
 
 if(WIN32)
     string(REPLACE "/GR" " " CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}")
diff --git a/src/msix/pack/AppxPackageWriter.cpp b/src/msix/pack/AppxPackageWriter.cpp
index 2f44c31c..0338dc9f 100644
--- a/src/msix/pack/AppxPackageWriter.cpp
+++ b/src/msix/pack/AppxPackageWriter.cpp
@@ -175,7 +175,7 @@ namespace MSIX {
         ULARGE_INTEGER end = { 0 };
         ThrowHrIfFailed(stream->Seek(start, StreamBase::Reference::END, &end));
         ThrowHrIfFailed(stream->Seek(start, StreamBase::Reference::START, nullptr));
-        std::uint64_t uncompressedSize = static_cast<std::uint64_t>(end.u.LowPart);
+        std::uint64_t uncompressedSize = static_cast<std::uint64_t>(end.QuadPart);
 
         std::string opcFileName;
         // Don't encode [Content Type].xml
diff --git a/src/test/msixtest/CMakeLists.txt b/src/test/msixtest/CMakeLists.txt
index ad80ee81..e5bb75df 100644
--- a/src/test/msixtest/CMakeLists.txt
+++ b/src/test/msixtest/CMakeLists.txt
@@ -14,6 +14,10 @@ if(WIN32)
     endif()
 endif()
 
+# Enable differentiation of based on being used in the tests. 
+# Keep usage of this to a minimum; it is primarily intended for Exceptions.hpp
+add_definitions(-DMSIX_TEST=1)
+
 set(MsixTestFiles)
 
 list(APPEND MsixTestFiles
@@ -81,7 +85,7 @@ else()
         )
 endif()
 
-target_include_directories(${PROJECT_NAME} PRIVATE ${MSIX_BINARY_ROOT}/src/msix ${MSIX_PROJECT_ROOT}/lib/catch2 ${CMAKE_CURRENT_SOURCE_DIR}/inc)
+target_include_directories(${PROJECT_NAME} PRIVATE ${MSIX_PROJECT_ROOT}/src/inc/public ${MSIX_PROJECT_ROOT}/lib/catch2 ${CMAKE_CURRENT_SOURCE_DIR}/inc ${MSIX_PROJECT_ROOT}/src/inc/shared)
 
 # Output test binaries into a test directory
 set_target_properties(${PROJECT_NAME} PROPERTIES
diff --git a/src/test/msixtest/api_packagewriter.cpp b/src/test/msixtest/api_packagewriter.cpp
index 8bae6d74..e5f5abc7 100644
--- a/src/test/msixtest/api_packagewriter.cpp
+++ b/src/test/msixtest/api_packagewriter.cpp
@@ -8,6 +8,7 @@
 #include "FileHelpers.hpp"
 #include "PackTestData.hpp"
 #include "macros.hpp"
+#include "StreamBase.hpp"
 
 #include <iostream>
 
@@ -350,3 +351,97 @@ TEST_CASE("Api_AppxPackageWriter_closed", "[api]")
             APPX_COMPRESSION_OPTION_NORMAL,
             fileStream.Get()));
 }
+
+class GeneratedEasilyCompressedFileStream final : public MSIX::StreamBase
+{
+public:
+    GeneratedEasilyCompressedFileStream(uint64_t size) : m_size(size) {}
+
+    // IStream
+    HRESULT STDMETHODCALLTYPE Seek(LARGE_INTEGER move, DWORD origin, ULARGE_INTEGER* newPosition) noexcept override try
+    {
+        // Determine new range relative position
+        LARGE_INTEGER newPos = { 0 };
+        switch (origin)
+        {
+        case Reference::CURRENT:
+            newPos.QuadPart = m_offset + move.QuadPart;
+            break;
+        case Reference::START:
+            newPos.QuadPart = move.QuadPart;
+            break;
+        case Reference::END:
+            newPos.QuadPart = m_size + move.QuadPart;
+            break;
+        }
+
+        // Constrain newPos to range relative values
+        if (newPos.QuadPart < 0)
+        {
+            m_offset = 0;
+        }
+        else
+        {
+            m_offset = std::min(static_cast<uint64_t>(newPos.QuadPart), m_size);
+        }
+
+        if (newPosition) { newPosition->QuadPart = m_offset; }
+        return static_cast<HRESULT>(MSIX::Error::OK);
+    } CATCH_RETURN();
+
+    HRESULT STDMETHODCALLTYPE Read(void* buffer, ULONG countBytes, ULONG* bytesRead) noexcept override try
+    {
+        uint64_t bytesToRead = std::min(m_size - m_offset, static_cast<uint64_t>(countBytes));
+        // We can't really fail so just put the value in directly.
+        if (bytesRead) { *bytesRead = static_cast<ULONG>(bytesToRead); }
+
+        while (bytesToRead)
+        {
+            uint64_t block = m_offset / DefaultBlockSize;
+            uint64_t endOfBlock = (block + 1) * DefaultBlockSize;
+            uint64_t bytesToWrite = std::min(endOfBlock, m_size) - m_offset;
+            bytesToWrite = std::min(bytesToWrite, bytesToRead);
+            memset(buffer, static_cast<int>(block % 256), static_cast<size_t>(bytesToWrite));
+
+            buffer = static_cast<void*>(static_cast<int8_t*>(buffer) + bytesToWrite);
+            m_offset += bytesToWrite;
+            bytesToRead -= bytesToWrite;
+        }
+
+        return static_cast<HRESULT>(MSIX::Error::OK);
+    } CATCH_RETURN();
+
+protected:
+    uint64_t m_size = 0;
+    uint64_t m_offset = 0;
+};
+
+// Test creating a valid msix package with a contained file that is larger than 4GB
+// The package itself will be much smaller; do not unpack the package from this test
+TEST_CASE("Api_AppxPackageWriter_file_over_4GB", "[api][.slow]")
+{
+    auto outputStream = MsixTest::StreamFile("test_package.msix", false, true);
+
+    MsixTest::ComPtr<IAppxPackageWriter> packageWriter;
+    InitializePackageWriter(outputStream.Get(), &packageWriter);
+
+    // Create stream to generate our very compressable data with more than 4GB of data
+    auto fileStream = MsixTest::ComPtr<IStream>::Make<GeneratedEasilyCompressedFileStream>(0x100000100);
+    REQUIRE_SUCCEEDED(packageWriter->AddPayloadFile(
+        L"largefile.bin",
+        TestConstants::ContentType.c_str(),
+        APPX_COMPRESSION_OPTION_NORMAL,
+        fileStream.Get()));
+
+    // Finalize package, create manifest stream
+    MsixTest::ComPtr<IStream> manifestStream;
+    MakeManifestStream(&manifestStream);
+    REQUIRE_SUCCEEDED(packageWriter->Close(manifestStream.Get()));
+
+    // Reopen the package, validates that the written package is readable
+    // return to the beginning
+    LARGE_INTEGER zero = { 0 };
+    REQUIRE_SUCCEEDED(outputStream.Get()->Seek(zero, STREAM_SEEK_SET, nullptr));
+    MsixTest::ComPtr<IAppxPackageReader> packageReader;
+    MsixTest::InitializePackageReader(outputStream.Get(), &packageReader);
+}
diff --git a/src/test/msixtest/inc/msixtest_int.hpp b/src/test/msixtest/inc/msixtest_int.hpp
index 21a12204..b11e900a 100644
--- a/src/test/msixtest/inc/msixtest_int.hpp
+++ b/src/test/msixtest/inc/msixtest_int.hpp
@@ -6,6 +6,7 @@
 #include "AppxPackaging.hpp"
 #include "MSIXWindows.hpp"
 #include "MsixErrors.hpp"
+#include "ComHelper.hpp"
 
 #include "msixtest.hpp"
 #include "macros.hpp"
@@ -116,72 +117,8 @@ namespace MsixTest {
     void InitializeBundleReader(const std::string& package, IAppxBundleReader** bundleReader);
     void InitializeManifestReader(const std::string& manifest, IAppxManifestReader** manifestReader);
 
-    template <class T>
-    class ComPtr
-    {
-    public:
-        // default ctor
-        ComPtr() = default;
-        explicit ComPtr(T* ptr) : m_ptr(ptr) { InternalAddRef(); }
-
-        ComPtr(const ComPtr& other) : m_ptr(other.m_ptr) { InternalAddRef(); }
-        ComPtr& operator=(const ComPtr& other) { InternalRelease(); m_ptr = other.m_ptr; InternalAddRef(); return *this; }
-
-        ComPtr(ComPtr&& other) : m_ptr(other.m_ptr) { other.m_ptr = nullptr; }
-        ComPtr& operator=(ComPtr&& other) { InternalRelease(); m_ptr = other.m_ptr; other.m_ptr = nullptr; return *this; }
-
-        ~ComPtr() { InternalRelease(); }
-
-        // For use instead of ComPtr<T> t(new Foo(...));
-        template<class U, class... Args>
-        static ComPtr<T> Make(Args&&... args)
-        {
-            ComPtr<T> result;
-            result.m_ptr = new U(std::forward<Args>(args)...);
-            return result;
-        }
-        
-        inline T* operator->() const { return m_ptr; }
-        inline T* Get() const { return m_ptr; }
-        T* Detach() 
-        {
-            T* temp = m_ptr;
-            m_ptr = nullptr;
-            return temp;
-        }
-
-        template <class U>
-        ComPtr<U> As() const
-        {
-            ComPtr<U> out;
-            REQUIRE_SUCCEEDED(m_ptr->QueryInterface(UuidOfImpl<U>::iid, reinterpret_cast<void**>(&out)));
-            return out;
-        }
-
-        inline T** operator&()
-        {   InternalRelease();
-            return &m_ptr;
-        }
-
-        bool Release()
-        {
-            return InternalRelease();
-        }
-
-    protected:
-        T* m_ptr = nullptr;
-
-        inline void InternalAddRef() { if (m_ptr) { m_ptr->AddRef(); } }
-        inline bool InternalRelease()
-        {
-            T* temp = m_ptr;
-            if (temp)
-            {   m_ptr = nullptr;
-                return (temp->Release() == 0);
-            }
-            return false;
-        }
-    };
+    // Use the product ComPtr; enables sharing without updating every qualified use.
+    using MSIX::ComPtr;
 
     // Helper class that creates a stream from a given file name.
     // toRead - true if the file already exists, false to create it
diff --git a/src/test/msixtest/msixtest.cpp b/src/test/msixtest/msixtest.cpp
index 3bc43012..767965ec 100644
--- a/src/test/msixtest/msixtest.cpp
+++ b/src/test/msixtest/msixtest.cpp
@@ -215,12 +215,10 @@ namespace MsixTest {
     {
         if (m_toDelete && (m_stream.Get() != nullptr))
         {
+            m_stream = nullptr;
             // best effort to delete the file. If someone else has a reference to this stream
             // and this object is deleted, the file WILL NOT be deleted.
-            if (m_stream.Release())
-            {
-                remove(m_fileName.c_str());
-            }
+            remove(m_fileName.c_str());
         }
     }
 }