diff --git a/eng/SourceBuild.props b/eng/SourceBuild.props
index bbf4b6996cea33..5e12f4af83cc37 100644
--- a/eng/SourceBuild.props
+++ b/eng/SourceBuild.props
@@ -39,7 +39,7 @@
       <InnerBuildArgs>$(InnerBuildArgs) /p:AdditionalRuntimeIdentifierParent=$(BaseOS)</InnerBuildArgs>
       <InnerBuildArgs Condition="'$(OfficialBuildId)' != ''">$(InnerBuildArgs) /p:OfficialBuildId=$(OfficialBuildId)</InnerBuildArgs>
       <InnerBuildArgs Condition="'$(ContinuousIntegrationBuild)' != ''">$(InnerBuildArgs) /p:ContinuousIntegrationBuild=$(ContinuousIntegrationBuild)</InnerBuildArgs>
-      <InnerBuildArgs Condition="'$(SourceBuildUseMonoRuntime)' == 'true'">$(InnerBuildArgs) /p:PrimaryRuntimeFlavor=Mono /p:RuntimeFlavor=Mono</InnerBuildArgs>
+      <InnerBuildArgs Condition="'$(SourceBuildUseMonoRuntime)' == 'true'">$(InnerBuildArgs) --usemonoruntime</InnerBuildArgs>
     </PropertyGroup>
   </Target>
 
diff --git a/eng/Subsets.props b/eng/Subsets.props
index ef9935e2407dc9..f1af6a47bfddcd 100644
--- a/eng/Subsets.props
+++ b/eng/Subsets.props
@@ -26,8 +26,12 @@
        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="'$(TargetArchitecture)' == 's390x' or '$(TargetArchitecture)' == 'ppc64le' or '$(TargetArchitecture)' == 'armv6' or '$(TargetsLinuxBionic)' == 'true'">Mono</PrimaryRuntimeFlavor>
+    <DefaultPrimaryRuntimeFlavor>CoreCLR</DefaultPrimaryRuntimeFlavor>
+    <DefaultPrimaryRuntimeFlavor Condition="'$(TargetArchitecture)' == 'armv6'">Mono</DefaultPrimaryRuntimeFlavor>
+    <DefaultPrimaryRuntimeFlavor Condition="'$(TargetArchitecture)' == 'ppc64le'">Mono</DefaultPrimaryRuntimeFlavor>
+    <DefaultPrimaryRuntimeFlavor Condition="'$(TargetArchitecture)' == 's390x'">Mono</DefaultPrimaryRuntimeFlavor>
+    <DefaultPrimaryRuntimeFlavor Condition="'$(TargetsLinuxBionic)' == 'true'">Mono</DefaultPrimaryRuntimeFlavor>
+    <PrimaryRuntimeFlavor Condition="'$(PrimaryRuntimeFlavor)' == ''">$(DefaultPrimaryRuntimeFlavor)</PrimaryRuntimeFlavor>
   </PropertyGroup>
 
   <PropertyGroup>
diff --git a/eng/build.ps1 b/eng/build.ps1
index 99f0864317f39a..fc2712fcafe512 100644
--- a/eng/build.ps1
+++ b/eng/build.ps1
@@ -17,6 +17,7 @@ Param(
   [ValidateSet("Debug","Release")][string][Alias('lc')]$librariesConfiguration,
   [ValidateSet("CoreCLR","Mono")][string][Alias('rf')]$runtimeFlavor,
   [ValidateSet("Debug","Release","Checked")][string][Alias('hc')]$hostConfiguration,
+  [switch]$usemonoruntime = $false,
   [switch]$ninja,
   [switch]$msbuild,
   [string]$cmakeargs,
@@ -51,6 +52,7 @@ function Get-Help() {
   Write-Host "  -subset (-s)                   Build a subset, print available subsets with -subset help."
   Write-Host "                                 '-subset' can be omitted if the subset is given as the first argument."
   Write-Host "                                 [Default: Builds the entire repo.]"
+  Write-Host "  -usemonoruntime                Product a .NET runtime with Mono as the underlying runtime."
   Write-Host "  -verbosity (-v)                MSBuild verbosity: q[uiet], m[inimal], n[ormal], d[etailed], and diag[nostic]."
   Write-Host "                                 [Default: Minimal]"
   Write-Host "  -vs                            Open the solution with Visual Studio using the locally acquired SDK."
@@ -251,6 +253,7 @@ foreach ($argument in $PSBoundParameters.Keys)
   {
     "runtimeConfiguration"   { $arguments += " /p:RuntimeConfiguration=$((Get-Culture).TextInfo.ToTitleCase($($PSBoundParameters[$argument])))" }
     "runtimeFlavor"          { $arguments += " /p:RuntimeFlavor=$($PSBoundParameters[$argument].ToLowerInvariant())" }
+    "usemonoruntime"         { $arguments += " /p:PrimaryRuntimeFlavor=Mono" }
     "librariesConfiguration" { $arguments += " /p:LibrariesConfiguration=$((Get-Culture).TextInfo.ToTitleCase($($PSBoundParameters[$argument])))" }
     "hostConfiguration"      { $arguments += " /p:HostConfiguration=$((Get-Culture).TextInfo.ToTitleCase($($PSBoundParameters[$argument])))" }
     "framework"              { $arguments += " /p:BuildTargetFramework=$($PSBoundParameters[$argument].ToLowerInvariant())" }
diff --git a/eng/build.sh b/eng/build.sh
index 14855d30b0f1c6..469fd9d06714b2 100755
--- a/eng/build.sh
+++ b/eng/build.sh
@@ -45,6 +45,7 @@ usage()
   echo "  --subset (-s)                   Build a subset, print available subsets with -subset help."
   echo "                                 '--subset' can be omitted if the subset is given as the first argument."
   echo "                                  [Default: Builds the entire repo.]"
+  echo "  --usemonoruntime                Product a .NET runtime with Mono as the underlying runtime."
   echo "  --verbosity (-v)                MSBuild verbosity: q[uiet], m[inimal], n[ormal], d[etailed], and diag[nostic]."
   echo "                                  [Default: Minimal]"
   echo ""
@@ -369,6 +370,11 @@ while [[ $# > 0 ]]; do
       shift 2
       ;;
 
+     -usemonoruntime)
+      arguments="$arguments /p:PrimaryRuntimeFlavor=Mono"
+      shift 1
+      ;;
+
      -librariesconfiguration|-lc)
       if [ -z ${2+x} ]; then
         echo "No libraries configuration supplied. See help (--help) for supported libraries configurations." 1>&2