diff --git a/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/TypeMapLazyDictionary.cs b/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/TypeMapLazyDictionary.cs
index a644947b73463e..e18c1ffdda8ab6 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/TypeMapLazyDictionary.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/TypeMapLazyDictionary.cs
@@ -192,11 +192,11 @@ private static unsafe CallbackContext CreateMaps(
             RuntimeAssembly? startingAssembly;
             if (AppContext.GetData("System.Runtime.InteropServices.TypeMappingEntryAssembly") is string entryAssemblyName)
             {
-                startingAssembly = Assembly.Load(entryAssemblyName) as RuntimeAssembly;
+                startingAssembly = (RuntimeAssembly?)Assembly.Load(entryAssemblyName);
             }
             else
             {
-                startingAssembly = Assembly.GetEntryAssembly() as RuntimeAssembly;
+                startingAssembly = (RuntimeAssembly?)Assembly.GetEntryAssembly();
             }
 
             if (startingAssembly is null)