diff --git a/src/libraries/Directory.Build.props b/src/libraries/Directory.Build.props
index f36f83de45246..914f8531e197a 100644
--- a/src/libraries/Directory.Build.props
+++ b/src/libraries/Directory.Build.props
@@ -3,9 +3,12 @@
     <SkipInferTargetOSName>true</SkipInferTargetOSName>
     <DisableArcadeTestFramework>true</DisableArcadeTestFramework>
 
+    <_projectDirName>$([System.IO.Path]::GetFileName('$(MSBuildProjectDirectory)'))</_projectDirName>
+    <IsReferenceAssembly Condition="'$(_projectDirName)' == 'ref'">true</IsReferenceAssembly>
+    <IsSourceProject Condition="'$(_projectDirName)' == 'src'">true</IsSourceProject>
+    <IsGeneratorProject Condition="'$(_projectDirName)' == 'gen'">true</IsGeneratorProject>
+
     <!-- Set OutDirName to change BaseOutputPath and BaseIntermediateOutputPath to include the ref subfolder. -->
-    <_sepChar>$([System.IO.Path]::DirectorySeparatorChar)</_sepChar>
-    <IsReferenceAssembly Condition="$(MSBuildProjectFullPath.Contains('$(_sepChar)ref$(_sepChar)'))">true</IsReferenceAssembly>
     <OutDirName Condition="'$(IsReferenceAssembly)' == 'true'">$(MSBuildProjectName)$(_sepChar)ref</OutDirName>
   </PropertyGroup>
 
@@ -14,7 +17,6 @@
 
   <PropertyGroup>
     <BeforeTargetFrameworkInferenceTargets>$(RepositoryEngineeringDir)BeforeTargetFrameworkInference.targets</BeforeTargetFrameworkInferenceTargets>
-    <IsSourceProject>$([System.Text.RegularExpressions.Regex]::IsMatch($(MSBuildProjectDirectory), 'src%24'))</IsSourceProject>
     <RuntimeGraph>$(LibrariesProjectRoot)OSGroups.json</RuntimeGraph>
     <ShouldUnsetParentConfigurationAndPlatform>false</ShouldUnsetParentConfigurationAndPlatform>
     <!-- Remove once is fixed: https://github.com/dotnet/roslyn/issues/42344 -->
@@ -65,8 +67,8 @@
   </PropertyGroup>
 
   <PropertyGroup>
-    <RunApiCompatForSrc>$(IsSourceProject)</RunApiCompatForSrc>
-    <RunMatchingRefApiCompat>$(IsSourceProject)</RunMatchingRefApiCompat>
+    <RunApiCompatForSrc>$([MSBuild]::ValueOrDefault('$(IsSourceProject)', 'false'))</RunApiCompatForSrc>
+    <RunMatchingRefApiCompat>$([MSBuild]::ValueOrDefault('$(IsSourceProject)', 'false'))</RunMatchingRefApiCompat>
     <ApiCompatEnforceOptionalRules>true</ApiCompatEnforceOptionalRules>
     <ApiCompatExcludeAttributeList>$(RepositoryEngineeringDir)DefaultGenApiDocIds.txt,$(RepositoryEngineeringDir)ApiCompatExcludeAttributes.txt</ApiCompatExcludeAttributeList>
   </PropertyGroup>
diff --git a/src/libraries/Directory.Build.targets b/src/libraries/Directory.Build.targets
index 142c9dc38faee..c7f90af0891af 100644
--- a/src/libraries/Directory.Build.targets
+++ b/src/libraries/Directory.Build.targets
@@ -44,7 +44,7 @@
 
   <!-- Libraries-specific binplacing properties -->
   <PropertyGroup>
-    <IsRuntimeAssembly Condition="'$(IsRuntimeAssembly)'=='' and '$(IsReferenceAssembly)' != 'true' and '$(BinPlaceRef)' != 'true' and '$(IsTestProject)' != 'true' and '$(IsTestSupportProject)' != 'true'">true</IsRuntimeAssembly>
+    <IsRuntimeAssembly Condition="'$(IsRuntimeAssembly)'=='' and '$(IsReferenceAssembly)' != 'true' and '$(BinPlaceRef)' != 'true' and '$(IsGeneratorProject)' != 'true' and '$(IsTestProject)' != 'true' and '$(IsTestSupportProject)' != 'true'">true</IsRuntimeAssembly>
     <!-- Try to determine if this is a simple library without a ref project.
          https://github.com/dotnet/runtime/issues/19584 is tracking cleaning this up -->
     <IsRuntimeAndReferenceAssembly Condition="'$(IsRuntimeAndReferenceAssembly)' == '' and '$(IsRuntimeAssembly)' == 'true' and Exists('$(LibrariesProjectRoot)$(MSBuildProjectName)') and !Exists('$(LibrariesProjectRoot)$(MSBuildProjectName)/ref') and !$(MSBuildProjectName.StartsWith('System.Private'))">true</IsRuntimeAndReferenceAssembly>