diff --git a/Source/Tools/Flax.Build/Build/Assembler.cs b/Source/Tools/Flax.Build/Build/Assembler.cs
index 26f19774e..da22b3865 100644
--- a/Source/Tools/Flax.Build/Build/Assembler.cs
+++ b/Source/Tools/Flax.Build/Build/Assembler.cs
@@ -153,7 +153,7 @@ namespace Flax.Build
 
             // Run the compilation
             using var memoryStream = new MemoryStream();
-            CSharpParseOptions parseOptions = CSharpParseOptions.Default.WithLanguageVersion(LanguageVersion.CSharp11).WithPreprocessorSymbols(PreprocessorSymbols);
+            CSharpParseOptions parseOptions = CSharpParseOptions.Default.WithLanguageVersion(LanguageVersion.CSharp9).WithPreprocessorSymbols(PreprocessorSymbols);
             var syntaxTrees = new List<SyntaxTree>();
             foreach (var sourceFile in SourceFiles)
             {