diff --git a/compiler/cpp/src/generate/t_csharp_generator.cc b/compiler/cpp/src/generate/t_csharp_generator.cc
index d9659e4..5d6fb16 100644
--- a/compiler/cpp/src/generate/t_csharp_generator.cc
+++ b/compiler/cpp/src/generate/t_csharp_generator.cc
@@ -1054,7 +1054,7 @@
   // Let's define the class first
   start_csharp_namespace(out);
 
-  indent(out) << "public abstract class " << tunion->get_name() << " : TAbstractBase {" << endl;
+  indent(out) << "public abstract partial class " << tunion->get_name() << " : TAbstractBase {" << endl;
 
   indent_up();