diff --git a/eng/Packages.props b/eng/Packages.props
index 8e3c5e1caac..c6b2eabb7a2 100644
--- a/eng/Packages.props
+++ b/eng/Packages.props
@@ -3,6 +3,20 @@
      eng/Versions.props / eng/Version.Details.props. Manually-pinned, single-use packages carry
      their literal version here directly (no indirection through eng/Versions.props). -->
 <Project>
+  <!-- Evaluate these after source-build has replaced the darc versions with the live runtime package version.
+       Defining the aliases in Versions.props freezes the pre-override value and can cause CPM downgrades or
+       prebuilt package usage. The floor only affects normal builds whose flowed version is below MSBuild's
+       minimum; source-build's live version wins when it is newer. -->
+  <PropertyGroup>
+    <SystemRuntimeCentralFloorVersion>10.0.9</SystemRuntimeCentralFloorVersion>
+    <SystemSecurityCryptographyXmlCentralVersion>$(SystemSecurityCryptographyXmlVersion)</SystemSecurityCryptographyXmlCentralVersion>
+    <SystemCollectionsImmutableCentralVersion>$(SystemCollectionsImmutableVersion)</SystemCollectionsImmutableCentralVersion>
+    <SystemReflectionMetadataCentralVersion>$(SystemReflectionMetadataVersion)</SystemReflectionMetadataCentralVersion>
+    <SystemSecurityCryptographyXmlCentralVersion Condition="'$(SystemSecurityCryptographyXmlVersion)' != '' and $([MSBuild]::VersionLessThan('$(SystemSecurityCryptographyXmlVersion)', '$(SystemRuntimeCentralFloorVersion)'))">$(SystemRuntimeCentralFloorVersion)</SystemSecurityCryptographyXmlCentralVersion>
+    <SystemCollectionsImmutableCentralVersion Condition="'$(SystemCollectionsImmutableVersion)' != '' and $([MSBuild]::VersionLessThan('$(SystemCollectionsImmutableVersion)', '$(SystemRuntimeCentralFloorVersion)'))">$(SystemRuntimeCentralFloorVersion)</SystemCollectionsImmutableCentralVersion>
+    <SystemReflectionMetadataCentralVersion Condition="'$(SystemReflectionMetadataVersion)' != '' and $([MSBuild]::VersionLessThan('$(SystemReflectionMetadataVersion)', '$(SystemRuntimeCentralFloorVersion)'))">$(SystemRuntimeCentralFloorVersion)</SystemReflectionMetadataCentralVersion>
+  </PropertyGroup>
+
   <ItemGroup>
     <!-- Optimization data (MIBC) — referenced via @(MIBCPackage) in Directory.Build.targets -->
     <PackageVersion Include="optimization.windows_nt-x86.mibc.runtime" Version="$(optimizationwindows_ntx86MIBCRuntimeVersion)" />
diff --git a/eng/Version.Details.xml b/eng/Version.Details.xml
index 589261ec4d5..ffe08b09761 100644
--- a/eng/Version.Details.xml
+++ b/eng/Version.Details.xml
@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
 <Dependencies>
-  <Source Uri="https://github.com/dotnet/dotnet" Mapping="fsharp" Sha="7cdb217445905f3342bbb0266a4497b9a014389a" BarId="326717" />
+  <Source Uri="https://github.com/dotnet/dotnet" Mapping="fsharp" Sha="da377e2093fdde18a0d36429a2644638d07685f6" BarId="328805" />
   <ProductDependencies>
     <Dependency Name="Microsoft.Build" Version="18.11.0-1.26423.1">
       <Uri>https://github.com/dotnet/msbuild</Uri>
diff --git a/eng/Versions.props b/eng/Versions.props
index 32cd8b7b8c9..f8996329d3b 100644
--- a/eng/Versions.props
+++ b/eng/Versions.props
@@ -14,7 +14,7 @@
   <PropertyGroup>
     <!-- Don't use the built in support for pre-release iteration. The nuget repack task doesn't support
          the iteration format at the moment. https://github.com/dotnet/arcade/issues/15919 -->
-    <FSharpPreReleaseIteration>1</FSharpPreReleaseIteration>
+    <FSharpPreReleaseIteration>2</FSharpPreReleaseIteration>
     <PreReleaseVersionLabel>rc$(FSharpPreReleaseIteration)</PreReleaseVersionLabel>
     <!-- F# Version components -->
     <FSMajorVersion>11</FSMajorVersion>