diff --git a/src/D2L.CodeStyle.Analyzers/Immutability/ImmutabilityContext.Factory.cs b/src/D2L.CodeStyle.Analyzers/Immutability/ImmutabilityContext.Factory.cs
index 5e9c9cfe..09af0dce 100644
--- a/src/D2L.CodeStyle.Analyzers/Immutability/ImmutabilityContext.Factory.cs
+++ b/src/D2L.CodeStyle.Analyzers/Immutability/ImmutabilityContext.Factory.cs
@@ -54,6 +54,7 @@ internal partial class ImmutabilityContext {
 			("System.Text.RegularExpressions.Regex", default),
 			("System.Text.UTF8Encoding", default),
 			("System.Threading.ReaderWriterLockSlim", default),
+			("System.Threading.SemaphoreSlim", default),
 			("System.TimeSpan", default),
 			("System.Type", default),
 			("System.Uri", default),