diff --git a/src/Generator/Generators/CSharp/CSharpSources.cs b/src/Generator/Generators/CSharp/CSharpSources.cs
index c513a3e3ff..8ed89aae63 100644
--- a/src/Generator/Generators/CSharp/CSharpSources.cs
+++ b/src/Generator/Generators/CSharp/CSharpSources.cs
@@ -149,6 +149,9 @@ group s by s.TemplatedDecl.TemplatedClass into template
                     UnindentAndWriteCloseBrace();
                 PopBlock(NewLineKind.BeforeNextBlock);
             }
+
+            if (Options.GenerationOutputMode == GenerationOutputMode.FilePerUnit)
+                Module.ExternalClassTemplateSpecializations.Clear();
         }
 
         public virtual void GenerateUsings()