diff --git a/appveyor.yml b/appveyor.yml
index 3729ea028..849b05a1d 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -16,6 +16,7 @@ matrix:
 image:
   - Visual Studio 2015
   - Visual Studio 2017
+  - MinGW  
     
 platform:
   - Win32
@@ -26,10 +27,13 @@ configuration: Release
 install:
   - set PATH=C:\Ruby24-x64\bin;%PATH%
   - set CMAKE_DEFINES -DASSIMP_WERROR=ON
+  - if [%COMPILER%]==[MinGW] set PATH=C:\MinGW\bin;%PATH%
   - if "%APPVEYOR_BUILD_WORKER_IMAGE%"=="Visual Studio 2015" set CMAKE_GENERATOR_NAME=Visual Studio 14 2015
   - if "%APPVEYOR_BUILD_WORKER_IMAGE%"=="Visual Studio 2017" set CMAKE_GENERATOR_NAME=Visual Studio 15 2017
   - if "%platform%"=="x64" set CMAKE_GENERATOR_NAME=%CMAKE_GENERATOR_NAME% Win64
   - cmake %CMAKE_DEFINES% -G "%CMAKE_GENERATOR_NAME%" .
+  # Rename sh.exe as sh.exe in PATH interferes with MinGW
+  - rename "C:\Program Files\Git\usr\bin\sh.exe" "sh2.exe"
   - set PATH=%PATH%;"C:\\Program Files (x86)\\Inno Setup 5"
   - ps: Invoke-WebRequest -Uri https://download.microsoft.com/download/5/7/b/57b2947c-7221-4f33-b35e-2fc78cb10df4/vc_redist.x64.exe -OutFile .\packaging\windows-innosetup\vc_redist.x64.exe
   - ps: Invoke-WebRequest -Uri https://download.microsoft.com/download/1/d/8/1d8137db-b5bb-4925-8c5d-927424a2e4de/vc_redist.x86.exe -OutFile .\packaging\windows-innosetup\vc_redist.x86.exe
diff --git a/code/Material/MaterialSystem.cpp b/code/Material/MaterialSystem.cpp
index d0b39093b..ecdf9942c 100644
--- a/code/Material/MaterialSystem.cpp
+++ b/code/Material/MaterialSystem.cpp
@@ -545,23 +545,7 @@ aiReturn aiMaterial::AddProperty (const aiString* pInput,
     unsigned int type,
     unsigned int index)
 {
-    // We don't want to add the whole buffer .. write a 32 bit length
-    // prefix followed by the zero-terminated UTF8 string.
-    // (HACK) I don't want to break the ABI now, but we definitely
-    // ought to change aiString::mLength to uint32_t one day.
-    if (sizeof(size_t) == 8) {
-        aiString copy = *pInput;
-        uint32_t* s = reinterpret_cast<uint32_t*>(&copy.length);
-        s[1] = static_cast<uint32_t>(pInput->length);
-
-        return AddBinaryProperty(s+1,
-            static_cast<unsigned int>(pInput->length+1+4),
-            pKey,
-            type,
-            index,
-            aiPTI_String);
-    }
-    ai_assert(sizeof(size_t)==4);
+    ai_assert(sizeof(ai_uint32)==4);
     return AddBinaryProperty(pInput,
         static_cast<unsigned int>(pInput->length+1+4),
         pKey,
diff --git a/code/glTF/glTFImporter.cpp b/code/glTF/glTFImporter.cpp
index e470050b9..9ecd742f6 100644
--- a/code/glTF/glTFImporter.cpp
+++ b/code/glTF/glTFImporter.cpp
@@ -266,7 +266,7 @@ void glTFImporter::ImportMeshes(glTF::Asset& r)
 
             aim->mName = mesh.id;
             if (mesh.primitives.size() > 1) {
-                size_t& len = aim->mName.length;
+                ai_uint32& len = aim->mName.length;
                 aim->mName.data[len] = '-';
                 len += 1 + ASSIMP_itoa10(aim->mName.data + len + 1, unsigned(MAXLEN - len - 1), p);
             }
diff --git a/code/glTF2/glTF2Importer.cpp b/code/glTF2/glTF2Importer.cpp
index d1871ce0e..9197f3b94 100644
--- a/code/glTF2/glTF2Importer.cpp
+++ b/code/glTF2/glTF2Importer.cpp
@@ -385,7 +385,7 @@ void glTF2Importer::ImportMeshes(glTF2::Asset& r)
             aim->mName = mesh.name.empty() ? mesh.id : mesh.name;
 
             if (mesh.primitives.size() > 1) {
-                size_t& len = aim->mName.length;
+                ai_uint32& len = aim->mName.length;
                 aim->mName.data[len] = '-';
                 len += 1 + ASSIMP_itoa10(aim->mName.data + len + 1, unsigned(MAXLEN - len - 1), p);
             }
diff --git a/include/assimp/types.h b/include/assimp/types.h
index 331b8cd03..e0a004c92 100644
--- a/include/assimp/types.h
+++ b/include/assimp/types.h
@@ -53,6 +53,7 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #include <stddef.h>
 #include <string.h>
 #include <limits.h>
+#include <stdint.h>
 
 // Our compile configuration
 #include "defs.h"
@@ -65,11 +66,15 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #include "matrix4x4.h"
 #include "quaternion.h"
 
+typedef int32_t ai_int32;
+typedef uint32_t ai_uint32 ;
+
 #ifdef __cplusplus
 #include <cstring>
 #include <new>      // for std::nothrow_t
 #include <string>   // for aiString::Set(const std::string&)
 
+
 namespace Assimp    {
     //! @cond never
 namespace Intern        {
@@ -379,7 +384,7 @@ struct aiString
     /** Binary length of the string excluding the terminal 0. This is NOT the
      *  logical length of strings containing UTF-8 multi-byte sequences! It's
      *  the number of bytes from the beginning of the string to its end.*/
-    size_t length;
+    ai_uint32 length;
 
     /** String buffer. Size limit is MAXLEN */
     char data[MAXLEN];