diff --git a/eng/Subsets.props b/eng/Subsets.props
index f9bde27cb9777..f26f40c7d7a05 100644
--- a/eng/Subsets.props
+++ b/eng/Subsets.props
@@ -35,14 +35,24 @@
     <_subset Condition="'$(Subset)' == ''">+$(DefaultSubsets)+</_subset>
   </PropertyGroup>
 
+  <!-- Determine the primary runtime flavor. This is usually CoreCLR, except on
+       platforms (like s390x) where only Mono is supported. The primary runtime
+       flavor is used to decide when to build the hosts and installers. -->
+  <PropertyGroup>
+    <PrimaryRuntimeFlavor>CoreCLR</PrimaryRuntimeFlavor>
+    <PrimaryRuntimeFlavor Condition="'$(TargetArchitecture)' == 's390x'">Mono</PrimaryRuntimeFlavor>
+  </PropertyGroup>
+
   <PropertyGroup>
     <RuntimeFlavor Condition="'$(TargetsMobile)' == 'true'">Mono</RuntimeFlavor>
     <RuntimeFlavor Condition="'$(RuntimeFlavor)' == '' and ($(_subset.Contains('+mono+')) or $(_subset.Contains('+mono.runtime+'))) and (!$(_subset.Contains('+clr+')) and !$(_subset.Contains('+clr.runtime+')))">Mono</RuntimeFlavor>
-    <RuntimeFlavor Condition="'$(RuntimeFlavor)' == ''">CoreCLR</RuntimeFlavor>
+    <RuntimeFlavor Condition="'$(RuntimeFlavor)' == ''">$(PrimaryRuntimeFlavor)</RuntimeFlavor>
   </PropertyGroup>
 
   <PropertyGroup>
     <DefaultCoreClrSubsets>clr.native+linuxdac+clr.corelib+clr.tools+clr.nativecorelib+clr.packages</DefaultCoreClrSubsets>
+    <!-- Even on platforms that do not support the CoreCLR runtime, we still want to build ilasm/ildasm. -->
+    <DefaultCoreClrSubsets Condition="'$(PrimaryRuntimeFlavor)' != 'CoreCLR'">clr.iltools+clr.packages</DefaultCoreClrSubsets>
 
     <DefaultMonoSubsets Condition="'$(MonoEnableLLVM)' == 'true' and '$(MonoLLVMDir)' == ''">mono.llvm+</DefaultMonoSubsets>
     <DefaultMonoSubsets Condition="'$(MonoAOTEnableLLVM)' == 'true' and '$(MonoAOTLLVMDir)' == ''">mono.llvm+</DefaultMonoSubsets>
@@ -58,8 +68,8 @@
 
     <DefaultHostSubsets>host.native+host.tools</DefaultHostSubsets>
     <DefaultHostSubsets Condition="'$(DotNetBuildFromSource)' != 'true'">$(DefaultHostSubsets)+host.pkg+host.tests</DefaultHostSubsets>
-    <DefaultHostSubsets Condition="'$(RuntimeFlavor)' == 'Mono'"></DefaultHostSubsets>
-    <DefaultHostSubsets Condition="'$(RuntimeFlavor)' == 'Mono' and '$(TargetsMobile)' != 'true'">host.native</DefaultHostSubsets>
+    <DefaultHostSubsets Condition="'$(RuntimeFlavor)' != '$(PrimaryRuntimeFlavor)'"></DefaultHostSubsets>
+    <DefaultHostSubsets Condition="'$(RuntimeFlavor)' != '$(PrimaryRuntimeFlavor)' and '$(TargetsMobile)' != 'true'">host.native</DefaultHostSubsets>
 
     <DefaultPacksSubsets>packs.product</DefaultPacksSubsets>
     <DefaultPacksSubsets Condition="'$(BuildMonoAOTCrossCompilerOnly)' != 'true'">$(DefaultPacksSubsets)+packs.tests</DefaultPacksSubsets>
@@ -225,7 +235,7 @@
 
   <ItemGroup Condition="$(_subset.Contains('+clr.packages+')) and '$(PgoInstrument)' != 'true'">
     <ProjectToBuild Include="$(CoreClrProjectRoot).nuget\coreclr-packages.proj" Pack="true" Category="clr" />
-    <ProjectToBuild Include="$(CoreClrProjectRoot)tools\dotnet-pgo\dotnet-pgo-pack.proj" Pack="true" BuildInParallel="false" Category="clr" Condition="'$(DotNetBuildFromSource)' != 'true'"/>
+    <ProjectToBuild Include="$(CoreClrProjectRoot)tools\dotnet-pgo\dotnet-pgo-pack.proj" Pack="true" BuildInParallel="false" Category="clr" Condition="'$(DotNetBuildFromSource)' != 'true' and '$(RuntimeFlavor)' != 'Mono'"/>
   </ItemGroup>
 
   <!-- Mono sets -->
@@ -317,16 +327,16 @@
       </ItemGroup>
       <ItemGroup Condition="'$(PgoInstrument)' != 'true'">
         <SharedFrameworkProjectToBuild Condition="'$(BuildMonoAOTCrossCompilerOnly)' != 'true'" Include="$(InstallerProjectRoot)pkg\sfx\Microsoft.NETCore.App\Microsoft.NETCore.App.Ref.sfxproj" />
-        <SharedFrameworkProjectToBuild Condition="'$(RuntimeFlavor)' != 'Mono'" Include="$(InstallerProjectRoot)pkg\sfx\Microsoft.NETCore.App\Microsoft.NETCore.App.Host.sfxproj" />
+        <SharedFrameworkProjectToBuild Condition="'$(RuntimeFlavor)' == '$(PrimaryRuntimeFlavor)'" Include="$(InstallerProjectRoot)pkg\sfx\Microsoft.NETCore.App\Microsoft.NETCore.App.Host.sfxproj" />
         <SharedFrameworkProjectToBuild Condition="'$(RuntimeFlavor)' != 'Mono'" Include="$(InstallerProjectRoot)pkg\sfx\Microsoft.NETCore.App\Microsoft.NETCore.App.Crossgen2.sfxproj" />
-        <SharedFrameworkProjectToBuild Condition="'$(RuntimeFlavor)' != 'Mono'" Include="$(InstallerProjectRoot)pkg\sfx\installers\dotnet-host.proj" />
-        <SharedFrameworkProjectToBuild Condition="'$(RuntimeFlavor)' != 'Mono'" Include="$(InstallerProjectRoot)pkg\sfx\installers\dotnet-hostfxr.proj" />
-        <SharedFrameworkProjectToBuild Condition="'$(RuntimeFlavor)' != 'Mono'" Include="$(InstallerProjectRoot)pkg\sfx\installers\dotnet-runtime-deps\*.proj" />
+        <SharedFrameworkProjectToBuild Condition="'$(RuntimeFlavor)' == '$(PrimaryRuntimeFlavor)'" Include="$(InstallerProjectRoot)pkg\sfx\installers\dotnet-host.proj" />
+        <SharedFrameworkProjectToBuild Condition="'$(RuntimeFlavor)' == '$(PrimaryRuntimeFlavor)'" Include="$(InstallerProjectRoot)pkg\sfx\installers\dotnet-hostfxr.proj" />
+        <SharedFrameworkProjectToBuild Condition="'$(RuntimeFlavor)' == '$(PrimaryRuntimeFlavor)'" Include="$(InstallerProjectRoot)pkg\sfx\installers\dotnet-runtime-deps\*.proj" />
         <SharedFrameworkProjectToBuild Condition="'$(MonoCrossAOTTargetOS)' != ''" Include="$(InstallerProjectRoot)pkg\sfx\Microsoft.NETCore.App\monocrossaot.sfxproj" Pack="true" />
       </ItemGroup>
       <ItemGroup>
         <SharedFrameworkProjectToBuild Condition="'$(BuildMonoAOTCrossCompilerOnly)' != 'true'" Include="$(InstallerProjectRoot)pkg\sfx\Microsoft.NETCore.App\Microsoft.NETCore.App.Runtime.sfxproj" />
-        <SharedFrameworkProjectToBuild Condition="'$(RuntimeFlavor)' != 'Mono'" Include="$(InstallerProjectRoot)pkg\sfx\bundle\Microsoft.NETCore.App.Bundle.bundleproj" />
+        <SharedFrameworkProjectToBuild Condition="'$(RuntimeFlavor)' == '$(PrimaryRuntimeFlavor)'" Include="$(InstallerProjectRoot)pkg\sfx\bundle\Microsoft.NETCore.App.Bundle.bundleproj" />
         <ProjectToBuild Include="@(SharedFrameworkProjectToBuild)" Category="packs" />
       </ItemGroup>
     </When>
diff --git a/src/coreclr/.nuget/coreclr-packages.proj b/src/coreclr/.nuget/coreclr-packages.proj
index 1347e06d5ff0a..5d6391b6124e2 100644
--- a/src/coreclr/.nuget/coreclr-packages.proj
+++ b/src/coreclr/.nuget/coreclr-packages.proj
@@ -5,12 +5,15 @@
     <ProjectReference Include="dotnet-ilverify\dotnet-ilverify.pkgproj" />
   </ItemGroup>
 
-  <ItemGroup Condition="'$(DotNetBuildFromSource)' != 'true'">
+  <ItemGroup Condition="'$(RuntimeFlavor)' == 'CoreCLR' and '$(DotNetBuildFromSource)' != 'true'">
     <ProjectReference Include="ILCompiler.Reflection.ReadyToRun.Experimental\ILCompiler.Reflection.ReadyToRun.Experimental.pkgproj" />
   </ItemGroup>
 
-  <ItemGroup>
+  <ItemGroup Condition="'$(RuntimeFlavor)' == 'CoreCLR'">
     <ProjectReference Include="Microsoft.NETCore.TestHost\Microsoft.NETCore.TestHost.proj" />
+  </ItemGroup>
+
+  <ItemGroup>
     <ProjectReference Include="Microsoft.NETCore.ILAsm\Microsoft.NETCore.ILAsm.proj" />
     <ProjectReference Include="Microsoft.NETCore.ILDAsm\Microsoft.NETCore.ILDAsm.proj" />
   </ItemGroup>
diff --git a/src/installer/pkg/projects/Microsoft.NETCore.DotNetAppHost/Microsoft.NETCore.DotNetAppHost.pkgproj b/src/installer/pkg/projects/Microsoft.NETCore.DotNetAppHost/Microsoft.NETCore.DotNetAppHost.pkgproj
index 73768455ceddc..8f078c7c1bb6e 100644
--- a/src/installer/pkg/projects/Microsoft.NETCore.DotNetAppHost/Microsoft.NETCore.DotNetAppHost.pkgproj
+++ b/src/installer/pkg/projects/Microsoft.NETCore.DotNetAppHost/Microsoft.NETCore.DotNetAppHost.pkgproj
@@ -6,13 +6,15 @@
 
   <ItemGroup>
     <NativeBinary Include="$(DotNetHostBinDir)/apphost$(ExeSuffix)" />
-    <NativeBinary Include="$(DotNetHostBinDir)/singlefilehost$(ExeSuffix)" />
     <NativeBinary Include="$(DotNetHostBinDir)/$(LibPrefix)nethost$(LibSuffix)" />
     <NativeBinary Include="$(DotNetHostBinDir)/$(LibPrefix)nethost$(StaticLibSuffix)" />
     <NativeBinary Include="$(DotNetHostBinDir)/coreclr_delegates.h" />
     <NativeBinary Include="$(DotNetHostBinDir)/hostfxr.h" />
     <NativeBinary Include="$(DotNetHostBinDir)/nethost.h" />
   </ItemGroup>
+  <ItemGroup Condition="'$(RuntimeFlavor)' != 'Mono'">
+    <NativeBinary Include="$(DotNetHostBinDir)/singlefilehost$(ExeSuffix)" />
+  </ItemGroup>
   <ItemGroup Condition="'$(TargetOS)' == 'windows'">
     <NativeBinary Include="$(DotNetHostBinDir)/comhost.dll" />
     <NativeBinary Include="$(DotNetHostBinDir)/ijwhost.dll" />
diff --git a/src/installer/pkg/sfx/Microsoft.NETCore.App/Directory.Build.targets b/src/installer/pkg/sfx/Microsoft.NETCore.App/Directory.Build.targets
index c570a22277456..61c12cb71a854 100644
--- a/src/installer/pkg/sfx/Microsoft.NETCore.App/Directory.Build.targets
+++ b/src/installer/pkg/sfx/Microsoft.NETCore.App/Directory.Build.targets
@@ -8,7 +8,7 @@
 
   <Target Name="ReturnProductVersion" Returns="$(Version)" />
 
-  <ItemGroup Condition="'$(RuntimeFlavor)' != 'Mono'">
+  <ItemGroup Condition="'$(RuntimeFlavor)' == '$(PrimaryRuntimeFlavor)'">
     <PackageReference Condition="'$(SkipInstallersPackageReference)' != 'true'" Include="Microsoft.DotNet.Build.Tasks.Installers" Version="$(MicrosoftDotNetBuildTasksInstallersVersion)" />
     <PackageReference Include="Microsoft.DotNet.Build.Tasks.Archives" Version="$(MicrosoftDotNetBuildTasksArchivesVersion)" />
   </ItemGroup>
diff --git a/src/installer/pkg/sfx/Microsoft.NETCore.App/Microsoft.NETCore.App.Host.sfxproj b/src/installer/pkg/sfx/Microsoft.NETCore.App/Microsoft.NETCore.App.Host.sfxproj
index ab948eb5ddbae..f32e7eb5e853b 100644
--- a/src/installer/pkg/sfx/Microsoft.NETCore.App/Microsoft.NETCore.App.Host.sfxproj
+++ b/src/installer/pkg/sfx/Microsoft.NETCore.App/Microsoft.NETCore.App.Host.sfxproj
@@ -2,7 +2,7 @@
   <Sdk Name="Microsoft.DotNet.SharedFramework.Sdk" />
 
   <PropertyGroup>
-    <SkipBuild Condition="'$(RuntimeFlavor)' == 'Mono'">true</SkipBuild>
+    <SkipBuild Condition="'$(RuntimeFlavor)' != '$(PrimaryRuntimeFlavor)'">true</SkipBuild>
     <PlatformPackageType>AppHostPack</PlatformPackageType>
     <UseTemplatedPlatformManifest>true</UseTemplatedPlatformManifest>
     <ArchiveName>dotnet-apphost-pack</ArchiveName>
@@ -21,13 +21,15 @@
 
   <ItemGroup>
     <NativeRuntimeAsset Include="$(DotNetHostBinDir)/apphost$(ExeSuffix)" />
-    <NativeRuntimeAsset Include="$(DotNetHostBinDir)/singlefilehost$(ExeSuffix)" />
     <NativeRuntimeAsset Include="$(DotNetHostBinDir)/$(LibPrefix)nethost$(LibSuffix)" />
     <NativeRuntimeAsset Include="$(DotNetHostBinDir)/$(LibPrefix)nethost$(StaticLibSuffix)" />
     <NativeRuntimeAsset Include="$(DotNetHostBinDir)/nethost.h" />
     <NativeRuntimeAsset Include="$(DotNetHostBinDir)/hostfxr.h" />
     <NativeRuntimeAsset Include="$(DotNetHostBinDir)/coreclr_delegates.h" />
   </ItemGroup>
+  <ItemGroup Condition="'$(RuntimeFlavor)' != 'Mono'">
+    <NativeRuntimeAsset Include="$(DotNetHostBinDir)/singlefilehost$(ExeSuffix)" />
+  </ItemGroup>
   <ItemGroup Condition="'$(TargetOS)' == 'windows'">
     <NativeRuntimeAsset Include="$(DotNetHostBinDir)/comhost.dll" />
     <NativeRuntimeAsset Include="$(DotNetHostBinDir)/ijwhost.dll" />
diff --git a/src/installer/pkg/sfx/Microsoft.NETCore.App/Microsoft.NETCore.App.Runtime.props b/src/installer/pkg/sfx/Microsoft.NETCore.App/Microsoft.NETCore.App.Runtime.props
index 3fe16b05bacc0..87aaf9d263ced 100644
--- a/src/installer/pkg/sfx/Microsoft.NETCore.App/Microsoft.NETCore.App.Runtime.props
+++ b/src/installer/pkg/sfx/Microsoft.NETCore.App/Microsoft.NETCore.App.Runtime.props
@@ -15,7 +15,7 @@
     <MacOSPackageDescription>The .NET Shared Framework</MacOSPackageDescription>
   </PropertyGroup>
 
-  <PropertyGroup Condition="'$(RuntimeFlavor)' == 'Mono'">
+  <PropertyGroup Condition="'$(RuntimeFlavor)' == 'Mono' and '$(RuntimeFlavor)' != '$(PrimaryRuntimeFlavor)'">
     <RuntimeSpecificFrameworkSuffix>Mono</RuntimeSpecificFrameworkSuffix>
   </PropertyGroup>
   <PropertyGroup Condition="'$(MonoEnableLLVM)' == 'true' and '$(RuntimeFlavor)' == 'Mono' and '$(TargetsMobile)' != 'true' and '$(TargetsBrowser)' != 'true'">
diff --git a/src/installer/pkg/sfx/bundle/Microsoft.NETCore.App.Bundle.bundleproj b/src/installer/pkg/sfx/bundle/Microsoft.NETCore.App.Bundle.bundleproj
index c69491f5044a0..90f8d4ad2a28f 100644
--- a/src/installer/pkg/sfx/bundle/Microsoft.NETCore.App.Bundle.bundleproj
+++ b/src/installer/pkg/sfx/bundle/Microsoft.NETCore.App.Bundle.bundleproj
@@ -5,7 +5,7 @@
       Name, used to generate the bundle upgrade code. Must stay the same to allow bundles in a given
       product band to upgrade in place.
     -->
-    <SkipBuild Condition="'$(RuntimeFlavor)' == 'Mono'">true</SkipBuild>
+    <SkipBuild Condition="'$(RuntimeFlavor)' != '$(PrimaryRuntimeFlavor)'">true</SkipBuild>
     <IsShipping Condition="'$(PgoInstrument)' == 'true'">false</IsShipping>
     <BundleInstallerUpgradeCodeSeed>.NET Core Shared Framework Bundle Installer</BundleInstallerUpgradeCodeSeed>
     <BundleThemeDirectory>$(MSBuildProjectDirectory)</BundleThemeDirectory>
diff --git a/src/installer/pkg/sfx/installers/dotnet-host.proj b/src/installer/pkg/sfx/installers/dotnet-host.proj
index 0963a7b89d8cc..953b0f4f8522f 100644
--- a/src/installer/pkg/sfx/installers/dotnet-host.proj
+++ b/src/installer/pkg/sfx/installers/dotnet-host.proj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.Build.NoTargets">
   <PropertyGroup>
-    <SkipBuild Condition="'$(RuntimeFlavor)' == 'Mono'">true</SkipBuild>
+    <SkipBuild Condition="'$(RuntimeFlavor)' != '$(PrimaryRuntimeFlavor)'">true</SkipBuild>
     <GenerateInstallers>true</GenerateInstallers>
     <InstallerName>dotnet-host</InstallerName>
     <InstallerName Condition="'$(TargetOS)' == 'OSX'">dotnet-host-internal</InstallerName>
diff --git a/src/installer/pkg/sfx/installers/dotnet-hostfxr.proj b/src/installer/pkg/sfx/installers/dotnet-hostfxr.proj
index 0edd1eaa9853d..2c5fa5d818886 100644
--- a/src/installer/pkg/sfx/installers/dotnet-hostfxr.proj
+++ b/src/installer/pkg/sfx/installers/dotnet-hostfxr.proj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.Build.NoTargets">
   <PropertyGroup>
-    <SkipBuild Condition="'$(RuntimeFlavor)' == 'Mono'">true</SkipBuild>
+    <SkipBuild Condition="'$(RuntimeFlavor)' != '$(PrimaryRuntimeFlavor)'">true</SkipBuild>
     <GenerateInstallers>true</GenerateInstallers>
     <ArchiveName>dotnet-hostfxr-internal</ArchiveName>
     <InstallerName>dotnet-hostfxr</InstallerName>
diff --git a/src/libraries/pkg/Directory.Build.props b/src/libraries/pkg/Directory.Build.props
index d31c32ee6470c..f1bb5ff9c315d 100644
--- a/src/libraries/pkg/Directory.Build.props
+++ b/src/libraries/pkg/Directory.Build.props
@@ -11,7 +11,7 @@
 
   <!-- Packages opt-in to automatic RID-specific builds by placing a *.RID.props next to their project
        that defines the OfficialBuildRID item: all RIDs targeted by the package -->
-  <Import Project="$(MSBuildProjectDirectory)\*.rids.props" Condition="'$(BuildingAnOfficialBuildLeg)' != 'true' or '$(RuntimeFlavor)' != 'Mono'"/>
+  <Import Project="$(MSBuildProjectDirectory)\*.rids.props" Condition="'$(BuildingAnOfficialBuildLeg)' != 'true' or '$(RuntimeFlavor)' == '$(PrimaryRuntimeFlavor)'"/>
 
   <!-- create the "BuildRID" item which is the set of all supported RIDs, with metadata.
        We'll add a RID for the current platform even if it isn't in the officially supported set -->