diff --git a/src/NativeProviders/MKL/capabilities.cpp b/src/NativeProviders/MKL/capabilities.cpp
index ae675c6b..270e1521 100644
--- a/src/NativeProviders/MKL/capabilities.cpp
+++ b/src/NativeProviders/MKL/capabilities.cpp
@@ -20,6 +20,11 @@ extern "C" {
 		case 0:	return 0;
 		case 1:	return -1;
 
+		case 4: return sizeof(size_t);    // 4 (x86), 8 (x64)
+		case 5: return sizeof(MKL_INT);   // 4 (both)
+		case 6: return sizeof(MKL_LONG);  // 4 (both)
+		case 7: return sizeof(MKL_INT64); // 8 (both)
+
 		// PLATFORM
 		case 8:
 #ifdef _M_IX86
diff --git a/src/NativeProviders/MKL/fft.cpp b/src/NativeProviders/MKL/fft.cpp
index 870e6e77..cd20a16b 100644
--- a/src/NativeProviders/MKL/fft.cpp
+++ b/src/NativeProviders/MKL/fft.cpp
@@ -6,63 +6,61 @@
 #include <float.h>
 #include "mkl_dfti.h"
 
-inline MKL_INT64 fft_free(DFTI_DESCRIPTOR_HANDLE* handle)
+inline MKL_LONG fft_free(DFTI_DESCRIPTOR_HANDLE* handle)
 {
-	MKL_LONG status = DftiFreeDescriptor(handle);
-	return static_cast<MKL_INT64>(status);
+	return DftiFreeDescriptor(handle);
 }
 
 template<typename Precision>
-inline MKL_INT64 fft_create_1d(DFTI_DESCRIPTOR_HANDLE* handle, const MKL_INT64 n, const Precision forward_scale, const Precision backward_scale, const DFTI_CONFIG_VALUE precision, const DFTI_CONFIG_VALUE domain)
+inline MKL_LONG fft_create_1d(DFTI_DESCRIPTOR_HANDLE* handle, const MKL_LONG n, const Precision forward_scale, const Precision backward_scale, const DFTI_CONFIG_VALUE precision, const DFTI_CONFIG_VALUE domain)
 {
-	MKL_LONG status = DftiCreateDescriptor(handle, precision, domain, 1, static_cast<MKL_LONG>(n));
+	MKL_LONG status = DftiCreateDescriptor(handle, precision, domain, 1, n);
 	DFTI_DESCRIPTOR_HANDLE descriptor = *handle;
 	if (0 == status) status = DftiSetValue(descriptor, DFTI_FORWARD_SCALE, forward_scale);
 	if (0 == status) status = DftiSetValue(descriptor, DFTI_BACKWARD_SCALE, backward_scale);
 	if (0 == status) status = DftiCommitDescriptor(descriptor);
-	return static_cast<MKL_INT64>(status);
+	return status;
 }
 
 template<typename Data, typename FFT>
-inline MKL_INT64 fft_compute(const DFTI_DESCRIPTOR_HANDLE handle, Data x[], FFT fft)
+inline MKL_LONG fft_compute(const DFTI_DESCRIPTOR_HANDLE handle, Data x[], FFT fft)
 {
-	MKL_LONG status = fft(handle, x);
-	return static_cast<MKL_INT64>(status);
+	return fft(handle, x);
 }
 
 extern "C" {
 
-	DLLEXPORT MKL_INT64 x_fft_free(DFTI_DESCRIPTOR_HANDLE* handle)
+	DLLEXPORT MKL_LONG x_fft_free(DFTI_DESCRIPTOR_HANDLE* handle)
 	{
 		return fft_free(handle);
 	}
 
-	DLLEXPORT MKL_INT64 z_fft_create(DFTI_DESCRIPTOR_HANDLE* handle, const MKL_INT64 n, const double forward_scale, const double backward_scale)
+	DLLEXPORT MKL_LONG z_fft_create(DFTI_DESCRIPTOR_HANDLE* handle, const MKL_LONG n, const double forward_scale, const double backward_scale)
 	{
 		return fft_create_1d(handle, n, forward_scale, backward_scale, DFTI_DOUBLE, DFTI_COMPLEX);
 	}
 
-	DLLEXPORT MKL_INT64 c_fft_create(DFTI_DESCRIPTOR_HANDLE* handle, const MKL_INT64 n, const float forward_scale, const float backward_scale)
+	DLLEXPORT MKL_LONG c_fft_create(DFTI_DESCRIPTOR_HANDLE* handle, const MKL_LONG n, const float forward_scale, const float backward_scale)
 	{
 		return fft_create_1d(handle, n, forward_scale, backward_scale, DFTI_SINGLE, DFTI_COMPLEX);
 	}
 
-	DLLEXPORT MKL_INT64 z_fft_forward(const DFTI_DESCRIPTOR_HANDLE handle, MKL_Complex16 x[])
+	DLLEXPORT MKL_LONG z_fft_forward(const DFTI_DESCRIPTOR_HANDLE handle, MKL_Complex16 x[])
 	{
 		return fft_compute(handle, x, DftiComputeForward);
 	}
 
-	DLLEXPORT MKL_INT64 c_fft_forward(const DFTI_DESCRIPTOR_HANDLE handle, MKL_Complex8 x[])
+	DLLEXPORT MKL_LONG c_fft_forward(const DFTI_DESCRIPTOR_HANDLE handle, MKL_Complex8 x[])
 	{
 		return fft_compute(handle, x, DftiComputeForward);
 	}
 
-	DLLEXPORT MKL_INT64 z_fft_backward(const DFTI_DESCRIPTOR_HANDLE handle, MKL_Complex16 x[])
+	DLLEXPORT MKL_LONG z_fft_backward(const DFTI_DESCRIPTOR_HANDLE handle, MKL_Complex16 x[])
 	{
 		return fft_compute(handle, x, DftiComputeBackward);
 	}
 
-	DLLEXPORT MKL_INT64 c_fft_backward(const DFTI_DESCRIPTOR_HANDLE handle, MKL_Complex8 x[])
+	DLLEXPORT MKL_LONG c_fft_backward(const DFTI_DESCRIPTOR_HANDLE handle, MKL_Complex8 x[])
 	{
 		return fft_compute(handle, x, DftiComputeBackward);
 	}
diff --git a/src/Numerics/Providers/Common/Mkl/SafeNativeMethods.cs b/src/Numerics/Providers/Common/Mkl/SafeNativeMethods.cs
index 0378e5c4..c336e8f6 100644
--- a/src/Numerics/Providers/Common/Mkl/SafeNativeMethods.cs
+++ b/src/Numerics/Providers/Common/Mkl/SafeNativeMethods.cs
@@ -384,25 +384,25 @@ namespace MathNet.Numerics.Providers.Common.Mkl
         #region FFT
 
         [DllImport(_DllName, ExactSpelling = true, SetLastError = false, CallingConvention = CallingConvention.Cdecl)]
-        internal static extern long x_fft_free([In] ref IntPtr handle);
+        internal static extern int x_fft_free([In] ref IntPtr handle);
 
         [DllImport(_DllName, ExactSpelling = true, SetLastError = false, CallingConvention = CallingConvention.Cdecl)]
-        internal static extern long z_fft_create([Out] out IntPtr handle, long n, double forward_scale, double backward_scale);
+        internal static extern int z_fft_create([Out] out IntPtr handle, int n, double forward_scale, double backward_scale);
 
         [DllImport(_DllName, ExactSpelling = true, SetLastError = false, CallingConvention = CallingConvention.Cdecl)]
-        internal static extern long c_fft_create([Out] out IntPtr handle, long n, float forward_scale, float backward_scale);
+        internal static extern int c_fft_create([Out] out IntPtr handle, int n, float forward_scale, float backward_scale);
 
         [DllImport(_DllName, ExactSpelling = true, SetLastError = false, CallingConvention = CallingConvention.Cdecl)]
-        internal static extern long z_fft_forward([In] IntPtr handle, [In, Out] Complex[] x);
+        internal static extern int z_fft_forward([In] IntPtr handle, [In, Out] Complex[] x);
 
         [DllImport(_DllName, ExactSpelling = true, SetLastError = false, CallingConvention = CallingConvention.Cdecl)]
-        internal static extern long c_fft_forward([In] IntPtr handle, [In, Out] Complex32[] x);
+        internal static extern int c_fft_forward([In] IntPtr handle, [In, Out] Complex32[] x);
 
         [DllImport(_DllName, ExactSpelling = true, SetLastError = false, CallingConvention = CallingConvention.Cdecl)]
-        internal static extern long z_fft_backward([In] IntPtr handle, [In, Out] Complex[] x);
+        internal static extern int z_fft_backward([In] IntPtr handle, [In, Out] Complex[] x);
 
         [DllImport(_DllName, ExactSpelling = true, SetLastError = false, CallingConvention = CallingConvention.Cdecl)]
-        internal static extern long c_fft_backward([In] IntPtr handle, [In, Out] Complex32[] x);
+        internal static extern int c_fft_backward([In] IntPtr handle, [In, Out] Complex32[] x);
 
         #endregion FFT