diff --git a/TESTGUIDE.md b/TESTGUIDE.md
index 844c4704894..e869e561e9f 100644
--- a/TESTGUIDE.md
+++ b/TESTGUIDE.md
@@ -22,9 +22,8 @@ The test cases for this suite reside next to the Visual F# Tools code, at `vsint
 In order to run all of the tests, you will need to install
 
 * [Perl](http://www.perl.org/get.html) (ActiveState Perl 5.16.3 is known to work fine)
-* [NUnit](http://nunit.org/?p=download) (2.6.3 is known to work fine)
 
-Perl and NUnit must be included in the `%PATH%` for the below steps to work.  It is also recommended that you run tests from an elevated command prompt, as there are a couple of test cases which modify the GAC, and this requires administrative privileges.
+Perl must be included in the `%PATH%` for the below steps to work.  It is also recommended that you run tests from an elevated command prompt, as there are a couple of test cases which modify the GAC, and this requires administrative privileges.
 
 Before running tests, make sure you have successfully built all required projects as specified in the 'Prepare For Tests' section of the [DEVGUIDE](DEVGUIDE.md).
 
diff --git a/packages.config b/packages.config
index f3c92a29a42..a7462f84250 100644
--- a/packages.config
+++ b/packages.config
@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
 <packages>
-  <package id="NUnit" version="2.6.3" targetFramework="net40" />
-  <package id="NUnit.Runners" version="2.6.3" />
+  <package id="NUnit" version="2.6.4" targetFramework="net40" />
+  <package id="NUnit.Runners" version="2.6.4" />
 </packages>
\ No newline at end of file
diff --git a/src/FSharpSource.targets b/src/FSharpSource.targets
index a2d6b3bcb89..0003b7f3487 100644
--- a/src/FSharpSource.targets
+++ b/src/FSharpSource.targets
@@ -746,10 +746,11 @@
     <Exec Command=".\.nuget\NuGet.exe restore packages.config -PackagesDirectory packages" WorkingDirectory="$(FSharpSourcesRoot)\.."/>
   </Target>
 
-  <Target Name="BeforeResolveReferences">
-    <CreateProperty Value="$(ProjectDir)..\..\..\packages\NUnit.2.6.3\lib\;$(ProjectDir)..\..\..\packages\NUnit.Runners.2.6.3\tools\lib\;$(AssemblySearchPaths)">
-      <Output TaskParameter="Value"
-              PropertyName="AssemblySearchPaths" />
-    </CreateProperty>
-  </Target>
+  <PropertyGroup>
+    <AssemblySearchPaths>
+      $(ProjectDir)..\..\..\packages\NUNIT.2.6.4\lib\;
+      $(ProjectDir)..\..\..\packages\NUnit.Runners.2.6.4\tools\lib\;
+      $(AssemblySearchPaths);
+    </AssemblySearchPaths>
+  </PropertyGroup>
 </Project>
diff --git a/src/fsharp/FSharp.Compiler.Unittests/FSharp.Compiler.Unittests.fsproj b/src/fsharp/FSharp.Compiler.Unittests/FSharp.Compiler.Unittests.fsproj
index 5a38e3aa85f..cc8599e4b94 100644
--- a/src/fsharp/FSharp.Compiler.Unittests/FSharp.Compiler.Unittests.fsproj
+++ b/src/fsharp/FSharp.Compiler.Unittests/FSharp.Compiler.Unittests.fsproj
@@ -43,11 +43,7 @@
     <WarningLevel>3</WarningLevel>
   </PropertyGroup>
   <ItemGroup>
-    <!-- need full name and SpecificVersion = true in order to convince msbuild to allow this reference when targeting portable47 -->
-    <Reference Include="nunit.framework, Version=2.6.3.13283, Culture=neutral, PublicKeyToken=96d09a1eb7f44a77" Condition="'$(TargetFramework)' != 'sl5' AND '$(TargetFramework)' != 'sl3-wp'" >
-        <SpecificVersion>true</SpecificVersion>
-        <HintPath>$(FSharpSourcesRoot)\..\packages\NUnit.2.6.3\lib\nunit.framework.dll</HintPath>
-    </Reference>
+    <Reference Include="nunit.framework" Condition="'$(TargetFramework)' != 'sl5' AND '$(TargetFramework)' != 'sl3-wp'"><Private>true</Private></Reference>
     <Reference Include="NUnitFramework" Condition="'$(TargetFramework)' == 'sl5' OR '$(TargetFramework)' == 'sl3-wp'" />
   </ItemGroup>
   <ItemGroup Condition="!$(TargetFramework.Contains('portable'))">
diff --git a/src/fsharp/FSharp.Core.Unittests/FSharp.Core.Unittests.fsproj b/src/fsharp/FSharp.Core.Unittests/FSharp.Core.Unittests.fsproj
index 51a498d46b8..bcb2e2433d8 100644
--- a/src/fsharp/FSharp.Core.Unittests/FSharp.Core.Unittests.fsproj
+++ b/src/fsharp/FSharp.Core.Unittests/FSharp.Core.Unittests.fsproj
@@ -48,10 +48,7 @@
   </PropertyGroup>
   <ItemGroup>
     <!-- need full name and SpecificVersion = true in order to convince msbuild to allow this reference when targeting portable47 -->
-    <Reference Include="nunit.framework, Version=2.6.3.13283, Culture=neutral, PublicKeyToken=96d09a1eb7f44a77" Condition="'$(TargetFramework)' != 'sl5' AND '$(TargetFramework)' != 'sl3-wp'" >
-        <SpecificVersion>true</SpecificVersion>
-        <HintPath>$(FSharpSourcesRoot)\..\packages\NUnit.2.6.3\lib\nunit.framework.dll</HintPath>
-    </Reference>
+    <Reference Include="nunit.framework, Version=2.6.4.14350, Culture=neutral, PublicKeyToken=96d09a1eb7f44a77" Condition="'$(TargetFramework)' != 'sl5' AND '$(TargetFramework)' != 'sl3-wp'"><Private>true</Private><SpecificVersion>true</SpecificVersion></Reference>
     <Reference Include="NUnitFramework" Condition="'$(TargetFramework)' == 'sl5' OR '$(TargetFramework)' == 'sl3-wp'" />
     <ProjectReference Include="$(FSharpSourcesRoot)\fsharp\FSharp.Core\FSharp.Core.fsproj">
       <Project>{DED3BBD7-53F4-428A-8C9F-27968E768605}</Project>
diff --git a/tests/RunTests.cmd b/tests/RunTests.cmd
index f0d09f8e565..f4cc148e83e 100644
--- a/tests/RunTests.cmd
+++ b/tests/RunTests.cmd
@@ -10,7 +10,7 @@ goto :USAGE
 
 :flavor_ok
 
-set nunitpath=%~dp0%..\packages\NUnit.Runners.2.6.3\tools\
+set nunitpath=%~dp0%..\packages\NUnit.Runners.2.6.4\tools\
 if not exist "%nunitpath%" (
     pushd %~dp0..
     .\.nuget\nuget.exe restore packages.config -PackagesDirectory packages
diff --git a/tests/fsharp/optimize/stats/stats.txt b/tests/fsharp/optimize/stats/stats.txt
index 676d5db65ad..86f4fdc7639 100644
--- a/tests/fsharp/optimize/stats/stats.txt
+++ b/tests/fsharp/optimize/stats/stats.txt
@@ -452,3 +452,4 @@ Tue 07/14/2009,  9:26:43.59, Microsoft.FSharp-TypeFunc, 0, Microsoft.FSharp-clas
 20/01/2010, 19:59:48.26, Microsoft.FSharp-TypeFunc, 0, Microsoft.FSharp-classes, 1368,  Microsoft.FSharp-methods, 5716, ,  Microsoft.FSharp-fields, 1933,  
 21/04/2010, 21:42:44.95, Microsoft.FSharp-TypeFunc, 0, Microsoft.FSharp-classes, 1376,  Microsoft.FSharp-methods, 5730, ,  Microsoft.FSharp-fields, 1945,  
 Sun 11/09/2014, 17:38:09.23, Microsoft.FSharp-TypeFunc, 0, Microsoft.FSharp-classes, 2504,  Microsoft.FSharp-methods, 8641, ,  Microsoft.FSharp-fields, 3827,  
+Sat 02/07/2015,  0:35:46.24, Microsoft.FSharp-TypeFunc, 0, Microsoft.FSharp-classes, 2557,  Microsoft.FSharp-methods, 8939, ,  Microsoft.FSharp-fields, 4018,