diff --git a/dir.props b/dir.props
index 3b5424e406bb..535db0a346c8 100644
--- a/dir.props
+++ b/dir.props
@@ -187,6 +187,12 @@
     -->
     <UseECMAKey>false</UseECMAKey>
 
+    <!--
+      Full signing with Open key doesn't work with Portable Csc.
+      https://github.com/dotnet/roslyn/issues/8210
+    -->
+    <UseOpenKey>false</UseOpenKey>
+
     <!--
       Mono currently doesn't include VB targets for portable, notably /lib/mono/xbuild/Microsoft/Portable/v4.5/Microsoft.Portable.VisualBasic.targets.
       Fixed in https://github.com/mono/mono/pull/1726.
diff --git a/src/System.Buffers/src/System.Buffers.csproj b/src/System.Buffers/src/System.Buffers.csproj
index fd75975d19ff..05b5813550db 100644
--- a/src/System.Buffers/src/System.Buffers.csproj
+++ b/src/System.Buffers/src/System.Buffers.csproj
@@ -6,8 +6,7 @@
     <ProjectGuid>{2ADDB484-6F57-4D71-A3FE-A57EC6329A2B}</ProjectGuid>
     <PackageTargetFramework>dotnet5.2</PackageTargetFramework>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <!-- Disable Open Key on cross plat since Roslyn doesn't support it yet. See issue: https://github.com/dotnet/roslyn/issues/8210 -->
-    <UseOpenKey Condition="'$(OsEnvironment)'=='Windows_NT'">true</UseOpenKey>
+    <UseOpenKey Condition="'$(UseOpenKey)'==''">true</UseOpenKey>
   </PropertyGroup>
   <!-- Default configurations to help VS understand the options -->
   <PropertyGroup Condition="'$(Configuration)|$(Platform)' == 'Debug|AnyCPU'" />
diff --git a/src/System.Diagnostics.DiagnosticSource/src/System.Diagnostics.DiagnosticSource.csproj b/src/System.Diagnostics.DiagnosticSource/src/System.Diagnostics.DiagnosticSource.csproj
index 8bc252714cf4..eb14bcba806f 100644
--- a/src/System.Diagnostics.DiagnosticSource/src/System.Diagnostics.DiagnosticSource.csproj
+++ b/src/System.Diagnostics.DiagnosticSource/src/System.Diagnostics.DiagnosticSource.csproj
@@ -7,8 +7,7 @@
     <AssemblyVersion>4.0.0.0</AssemblyVersion>
     <DocumentationFile>$(OutputPath)$(AssemblyName).xml</DocumentationFile>
     <PackageTargetFramework>dotnet5.2</PackageTargetFramework>
-    <!-- Disable Open Key on cross plat since Roslyn doesn't support it yet. See issue: https://github.com/dotnet/roslyn/issues/8210 -->
-    <UseOpenKey Condition="'$(OsEnvironment)'=='Windows_NT'">true</UseOpenKey>
+    <UseOpenKey Condition="'$(UseOpenKey)'==''">true</UseOpenKey>
   </PropertyGroup>
   <!-- Default configurations to help VS understand the configurations -->
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
diff --git a/src/System.Text.Encodings.Web/src/System.Text.Encodings.Web.csproj b/src/System.Text.Encodings.Web/src/System.Text.Encodings.Web.csproj
index 71d5ce04c2a8..c32ddc97adb4 100644
--- a/src/System.Text.Encodings.Web/src/System.Text.Encodings.Web.csproj
+++ b/src/System.Text.Encodings.Web/src/System.Text.Encodings.Web.csproj
@@ -8,8 +8,7 @@
     <AssemblyVersion>4.0.0.0</AssemblyVersion>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <PackageTargetFramework>dotnet5.1</PackageTargetFramework>
-    <!-- Disable Open Key on cross plat since Roslyn doesn't support it yet. See issue: https://github.com/dotnet/roslyn/issues/8210 -->
-    <UseOpenKey Condition="'$(OsEnvironment)'=='Windows_NT'">true</UseOpenKey>
+    <UseOpenKey Condition="'$(UseOpenKey)'==''">true</UseOpenKey>
   </PropertyGroup>
   <!-- Default configurations to help VS understand the configurations -->
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
diff --git a/src/System.Threading.Tasks.Extensions/src/System.Threading.Tasks.Extensions.csproj b/src/System.Threading.Tasks.Extensions/src/System.Threading.Tasks.Extensions.csproj
index 0ee31bcdbc0d..d3d2d136b6bf 100644
--- a/src/System.Threading.Tasks.Extensions/src/System.Threading.Tasks.Extensions.csproj
+++ b/src/System.Threading.Tasks.Extensions/src/System.Threading.Tasks.Extensions.csproj
@@ -7,8 +7,7 @@
     <AssemblyVersion>4.0.0.0</AssemblyVersion>
     <DocumentationFile>$(OutputPath)$(AssemblyName).xml</DocumentationFile>
     <PackageTargetFramework>dotnet5.1</PackageTargetFramework>
-    <!-- Disable Open Key on cross plat since Roslyn doesn't support it yet. See issue: https://github.com/dotnet/roslyn/issues/8210 -->
-    <UseOpenKey Condition="'$(OsEnvironment)'=='Windows_NT'">true</UseOpenKey>
+    <UseOpenKey Condition="'$(UseOpenKey)'==''">true</UseOpenKey>
   </PropertyGroup>
   <!-- Default configurations to help VS understand the configurations -->
   <PropertyGroup Condition="'$(Configuration)|$(Platform)' == 'Debug|AnyCPU'" />