diff --git a/runtime/CSharp/Antlr4.Runtime/Atn/SemanticContext.cs b/runtime/CSharp/Antlr4.Runtime/Atn/SemanticContext.cs
index a2b21e7cb..6a6dc31e0 100644
--- a/runtime/CSharp/Antlr4.Runtime/Atn/SemanticContext.cs
+++ b/runtime/CSharp/Antlr4.Runtime/Atn/SemanticContext.cs
@@ -392,7 +392,11 @@ namespace Antlr4.Runtime.Atn
                 Collections.EmptyList<PrecedencePredicate>();
 
             List<PrecedencePredicate> result = collection.OfType<PrecedencePredicate>().ToList();
+#if NET_4_0
             collection.ExceptWith(result);
+#else
+            collection.ExceptWith(result.Cast<SemanticContext>());
+#endif
             return result;
         }
     }