diff --git a/packages.config b/packages.config
index 6195af6c9e1f174cb089dc80993d020329799648..43bff474ebf7de6fdf113a3d80f1846dab7b99a7 100644
--- a/packages.config
+++ b/packages.config
@@ -42,7 +42,7 @@
   <package id="FSharp.Compiler.Tools" version="4.1.5"/>
 
   <!-- Frozen portable library versions of FSharp.Core.dll (simply a renamed fsharp.core.4.1.18-->
-  <package id="Microsoft.Portable.FSharp.Core" version="4.1.18"/>
+  <package id="Microsoft.Portable.FSharp.Core" version="4.1.20"/>
 
   <!-- FSharp.Data is used in some of the scripts ued for the coreclr build -->
   <package id="FSharp.Data" version="2.2.5" />
diff --git a/setup/FSharp.SDK/component-groups/Runtime_LangPack.wxs b/setup/FSharp.SDK/component-groups/Runtime_LangPack.wxs
index 633cb063bb835ab52d9722c1ad55431a703a170c..d1efbb46935f1472edead75e979b22af3ac28821 100644
--- a/setup/FSharp.SDK/component-groups/Runtime_LangPack.wxs
+++ b/setup/FSharp.SDK/component-groups/Runtime_LangPack.wxs
@@ -52,22 +52,22 @@
       </DirectoryRef>
       <DirectoryRef Id="ReferenceAssemblies_Microsoft_FSharp_NETPortable_3.47.41.0_$(var.LocaleId)">
         <Component Id="Runtime_LangPack_3.47.41.0_FSharp.Core_LangPack" Transitive="yes" Guid="$(fsharp.guid(Runtime_LangPack_3.47.41.0_FSharp.Core_LangPack, $(var.LocaleCode)))">
-          <File Id="Runtime_LangPack_3.47.41._FSharp.Core.resources.dll" Source="$(var.BinariesDir)\portable47\bin\localize\$(var.LocaleCode)\FSharp.Core.resources.dll" KeyPath="yes" />
+          <File Id="Runtime_LangPack_3.47.41._FSharp.Core.resources.dll" Source="$(var.BinariesDir)\profiles\portable-net45%2Bsl5%2Bnetcore45\localize\$(var.LocaleCode)\FSharp.Core.resources.dll" KeyPath="yes" />
         </Component>
       </DirectoryRef>
       <DirectoryRef Id="ReferenceAssemblies_Microsoft_FSharp_NETCore_3.7.41.0_$(var.LocaleId)">
         <Component Id="Runtime_LangPack_3.7.41.0_FSharp.Core_LangPack" Transitive="yes" Guid="$(fsharp.guid(Runtime_LangPack_3.7.41.0_FSharp.Core_LangPack, $(var.LocaleCode)))">
-          <File Id="Runtime_LangPack_3.7.41.0_FSharp.Core.resources.dll" Source="$(var.BinariesDir)\portable7\bin\localize\$(var.LocaleCode)\FSharp.Core.resources.dll" KeyPath="yes" />
+          <File Id="Runtime_LangPack_3.7.41.0_FSharp.Core.resources.dll" Source="$(var.BinariesDir)\profiles\portable-net45%2Bnetcore45\localize\$(var.LocaleCode)\FSharp.Core.resources.dll" KeyPath="yes" />
         </Component>
       </DirectoryRef>
       <DirectoryRef Id="ReferenceAssemblies_Microsoft_FSharp_NETCore_3.78.41.0_$(var.LocaleId)">
         <Component Id="Runtime_LangPack_3.78.41.0_FSharp.Core_LangPack" Transitive="yes" Guid="$(fsharp.guid(Runtime_LangPack_3.78.41.0_FSharp.Core_LangPack, $(var.LocaleCode)))">
-          <File Id="Runtime_LangPack_3.78.41.0_FSharp.Core.resources.dll" Source="$(var.BinariesDir)\portable78\bin\localize\$(var.LocaleCode)\FSharp.Core.resources.dll" KeyPath="yes" />
+          <File Id="Runtime_LangPack_3.78.41.0_FSharp.Core.resources.dll" Source="$(var.BinariesDir)\profiles\portable-net45%2Bnetcore45%2Bwp8\localize\$(var.LocaleCode)\FSharp.Core.resources.dll" KeyPath="yes" />
         </Component>
       </DirectoryRef>
       <DirectoryRef Id="ReferenceAssemblies_Microsoft_FSharp_NETCore_3.259.41.0_$(var.LocaleId)">
         <Component Id="Runtime_LangPack_3.259.41.0_FSharp.Core_LangPack" Transitive="yes" Guid="$(fsharp.guid(Runtime_LangPack_3.259.41.0_FSharp.Core_LangPack, $(var.LocaleCode)))">
-          <File Id="Runtime_LangPack_3.259.41.0_FSharp.Core.resources.dll" Source="$(var.BinariesDir)\portable259\bin\localize\$(var.LocaleCode)\FSharp.Core.resources.dll" KeyPath="yes" />
+          <File Id="Runtime_LangPack_3.259.41.0_FSharp.Core.resources.dll" Source="$(var.BinariesDir)\profiles\portable-net45%2Bnetcore45%2Bwpa81%2Bwp8\localize\$(var.LocaleCode)\FSharp.Core.resources.dll" KeyPath="yes" />
         </Component>
       </DirectoryRef>
 
diff --git a/src/FSharpSource.Settings.targets b/src/FSharpSource.Settings.targets
index 343619149b7aa31551faa90b40f17032074ca429..671a2320e705b0bde996600496081cca5f62961e 100644
--- a/src/FSharpSource.Settings.targets
+++ b/src/FSharpSource.Settings.targets
@@ -31,7 +31,7 @@
     <BuildToolsTargets45>true</BuildToolsTargets45>
     <WarningsAsErrors />
     <FX_NO_LOADER Condition=" '$(FX_NO_LOADER)'==''">false</FX_NO_LOADER>
-    
+
     <RoslynVersion>2.0.0</RoslynVersion>
     <RoslynVSBinariesVersion>15.0</RoslynVSBinariesVersion>
     <RoslynVSPackagesVersion>15.0.26201</RoslynVSPackagesVersion>
@@ -44,8 +44,10 @@
     <IntermediateOutputPath>obj\$(Configuration)\$(TargetDotnetProfile)\</IntermediateOutputPath>
     <IntermediateOutputPath Condition="'$(PortableProfileBeingReferenced)' != ''">obj\$(Configuration)\$(TargetDotnetProfile)\$(PortableProfileBeingReferenced)\</IntermediateOutputPath>
 
-    <FSharpCore41Version>4.1.18</FSharpCore41Version>
-    <FSharpCore42Version>4.2.1</FSharpCore42Version>
+    <FSharpCore41TargetVersion>4.1.18</FSharpCore41TargetVersion>
+    <FSharpCore41FrozenPortableVersion>4.1.20</FSharpCore41FrozenPortableVersion>
+    <FSharpCore41FrozenPortableTargetVersion>4.1.21</FSharpCore41FrozenPortableTargetVersion>
+    <FSharpCore42TargetVersion>4.2.2</FSharpCore42TargetVersion>
   </PropertyGroup>
 
   <PropertyGroup Condition="'$(MonoPackaging)' != 'true' AND '$(OS)' != 'Unix'">
diff --git a/src/fsharp/FSharp.Core.nuget/FSharp.Core.nuget.proj b/src/fsharp/FSharp.Core.nuget/FSharp.Core.nuget.proj
index e2e2ceab809663c18c451deff3c70af2c63c4d6b..6373fc3fb3e939d9a68de67a4bacbee3728b1df2 100644
--- a/src/fsharp/FSharp.Core.nuget/FSharp.Core.nuget.proj
+++ b/src/fsharp/FSharp.Core.nuget/FSharp.Core.nuget.proj
@@ -18,6 +18,7 @@
   <ItemGroup>
     <PackageNuspec Include="FSharp.Core.4.2.xxx.nuspec" />
     <PackageNuspec Include="FSharp.Core.4.1.xxx.nuspec" />
+    <PackageNuspec Include="Microsoft.Portable.FSharp.Core.4.1.xxx.nuspec" />
   </ItemGroup>
 
   <ItemGroup>
@@ -36,10 +37,10 @@
 
   <Target Name="CopyFiles">
     <ItemGroup>
-        <Profiles Include="$(NugetLocalPackagesDir)\Microsoft.Portable.FSharp.Core.4.1.18\lib\*\*.*" 
-                  Exclude="$(NugetLocalPackagesDir)\Microsoft.Portable.FSharp.Core.4.1.18\lib\net45\*\*.*;$(NugetLocalPackagesDir)\Microsoft.Portable.FSharp.Core.4.1.18\lib\netstandard1.6\*\*.*" />
+        <Profiles Include="$(NugetLocalPackagesDir)\Microsoft.Portable.FSharp.Core.$(FSharpCore41FrozenPortableVersion)\lib\**\*.*" 
+                  Exclude="$(NugetLocalPackagesDir)\Microsoft.Portable.FSharp.Core.$(FSharpCore41FrozenPortableVersion)\lib\net45\**\*.*;$(NugetLocalPackagesDir)\Microsoft.Portable.FSharp.Core.$(FSharpCore41FrozenPortableVersionm)\lib\netstandard1.6\**\*.*" />
     </ItemGroup>
-    <Copy SourceFiles="@(Profiles)" DestinationFolder="$(FSharpSourcesRoot)\..\$(Configuration)\profiles\%(RecursiveDir)" />
+    <Copy SourceFiles="@(Profiles)" DestinationFolder="$(FSharpSourcesRoot)\..\$(Configuration)\%(RecursiveDir)" />
   </Target>
 
   <Target Name="nugetpackfsharpcore"
@@ -50,10 +51,16 @@
 
     <PropertyGroup>
       <PackageVersion>X.X.XXX</PackageVersion>
-      <PackageVersion Condition="'@(PackageNuspec)' == 'FSharp.Core.4.1.xxx.nuspec'">$(FSharpCore41Version)</PackageVersion>
+
+      <PackageVersion Condition="'@(PackageNuspec)' == 'FSharp.Core.4.1.xxx.nuspec'">$(FSharpCore41TargetVersion)</PackageVersion>
       <PackageMajorVersion Condition="'@(PackageNuspec)' == 'FSharp.Core.4.1.xxx.nuspec'">4.1</PackageMajorVersion>
-      <PackageVersion Condition="'@(PackageNuspec)' == 'FSharp.Core.4.2.xxx.nuspec'">$(FSharpCore42Version)</PackageVersion>
+
+      <PackageVersion Condition="'@(PackageNuspec)' == 'FSharp.Core.4.2.xxx.nuspec'">$(FSharpCore42TargetVersion)</PackageVersion>
       <PackageMajorVersion Condition="'@(PackageNuspec)' == 'FSharp.Core.4.2.xxx.nuspec'">4.2</PackageMajorVersion>
+
+      <PackageVersion Condition="'@(PackageNuspec)' == 'Microsoft.Portable.FSharp.Core.4.1.xxx.nuspec'">$(FSharpCore41FrozenPortableTargetVersion)</PackageVersion>
+      <PackageMajorVersion Condition="'@(PackageNuspec)' == 'Microsoft.Portable.FSharp.Core.4.1.xxx.nuspec'">4.1</PackageMajorVersion>
+
       <PackageProperties>-prop "licenseUrl=$(PackageLicenceUrl)" -prop "version=$(PackageVersion)" -prop "authors=$(PackageAuthors)" -prop "projectUrl=$(PackageProjectUrl)" -prop "tags=$(PackageTags)"</PackageProperties>
     </PropertyGroup>
 
diff --git a/src/fsharp/FSharp.Core.nuget/Microsoft.Portable.FSharp.Core.4.1.xxx.nuspec b/src/fsharp/FSharp.Core.nuget/Microsoft.Portable.FSharp.Core.4.1.xxx.nuspec
new file mode 100644
index 0000000000000000000000000000000000000000..128b62cb3fdcef4be013128cd7ecd713ec65133a
--- /dev/null
+++ b/src/fsharp/FSharp.Core.nuget/Microsoft.Portable.FSharp.Core.4.1.xxx.nuspec
@@ -0,0 +1,27 @@
+<?xml version="1.0"?>
+<package xmlns="http://schemas.microsoft.com/packaging/2012/06/nuspec.xsd">
+    <metadata>
+        <!-- rename to FSharp.Core when done -->
+        <id>Microsoft.Portable.FSharp.Core</id>
+        <description>Frozen portable profiles</description>
+        <language>en-US</language>
+        <requireLicenseAcceptance>false</requireLicenseAcceptance>
+        <version>$version$</version>
+        <authors>$authors$</authors>
+        <licenseUrl>$licenseUrl$</licenseUrl>
+        <projectUrl>$projectUrl$</projectUrl>
+        <tags>$tags$</tags>
+        <dependencies></dependencies>
+    </metadata>
+    <files>
+        <file src="profiles/net20/**/**" target="lib/" />
+        <file src="profiles/net40/**/**" target="lib/" />
+        <file src="profiles/portable-net45+monoandroid10+monotouch10+xamarinios10/**/**" target="lib/" />
+        <file src="profiles/portable-net45+netcore45/**/**"                              target="lib/" />
+        <file src="profiles/portable-net45+netcore45+wp8/**/**"                          target="lib/" />
+        <file src="profiles/portable-net45+netcore45+wpa81+wp8/**/**"                    target="lib/" />
+        <file src="profiles/portable-net45+sl5+netcore45/**/**"                          target="lib/" />
+        <file src="profiles/xamarinmac20/**/**"                                          target="lib/" />
+
+    </files>
+</package>
diff --git a/src/fsharp/FSharp.Core/FSharp.Core.fsproj b/src/fsharp/FSharp.Core/FSharp.Core.fsproj
index 6fd7e1ba0901ab268e2928b56d844e74eb2ebb1b..15dcfc5ab4c2a57fc0205ff68fbc58981015e252 100644
--- a/src/fsharp/FSharp.Core/FSharp.Core.fsproj
+++ b/src/fsharp/FSharp.Core/FSharp.Core.fsproj
@@ -276,7 +276,7 @@
           Outputs='$(FSharpSourcesRoot)\..\$(Configuration)\artifacts\"%(PackageNuspec.Filename)).nupkg'>
 
     <PropertyGroup>
-      <PackageProperties>-prop "licenseUrl=$(PackageLicenceUrl)" -prop "version=$(FSharpCore42Version)" -prop "authors=$(PackageAuthors)" -prop "projectUrl=$(PackageProjectUrl)" -prop "tags=$(PackageTags)"</PackageProperties>
+      <PackageProperties>-prop "licenseUrl=$(PackageLicenceUrl)" -prop "version=$(FSharpCore42TargetVersion)" -prop "authors=$(PackageAuthors)" -prop "projectUrl=$(PackageProjectUrl)" -prop "tags=$(PackageTags)"</PackageProperties>
     </PropertyGroup>
 
     <MakeDir Directories="$(FSharpSourcesRoot)\..\artifacts" />