diff --git a/Source/Tools/Flax.Build/Build/Assembler.cs b/Source/Tools/Flax.Build/Build/Assembler.cs
index 3a798144d..26f19774e 100644
--- a/Source/Tools/Flax.Build/Build/Assembler.cs
+++ b/Source/Tools/Flax.Build/Build/Assembler.cs
@@ -39,15 +39,20 @@ namespace Flax.Build
         public readonly List<string> SourceFiles = new List<string>();
 
         /// <summary>
-        /// The external user assembly references to use while compiling
+        /// The external user assembly references to use while compiling.
         /// </summary>
         public readonly List<Assembly> Assemblies = new List<Assembly>();
 
         /// <summary>
-        /// The external user assembly file names to use while compiling
+        /// The external user assembly file names to use while compiling.
         /// </summary>
         public readonly List<string> References = new List<string>();
 
+        /// <summary>
+        /// The C# preprocessor symbols to use while compiling.
+        /// </summary>
+        public readonly List<string> PreprocessorSymbols = new List<string>();
+
         public Assembler(List<string> sourceFiles, string cacheFolderPath = null)
         {
             SourceFiles.AddRange(sourceFiles);
@@ -127,10 +132,11 @@ namespace Flax.Build
                 if (!assembly.IsDynamic)
                     references.Add(assembly.Location);
             }
-            references.Add(Path.Combine(Directory.GetParent(DefaultReferences[0].Location).FullName, "System.dll"));
-            references.Add(Path.Combine(Directory.GetParent(DefaultReferences[0].Location).FullName, "System.Runtime.dll"));
-            references.Add(Path.Combine(Directory.GetParent(DefaultReferences[0].Location).FullName, "System.Collections.dll"));
-            references.Add(Path.Combine(Directory.GetParent(DefaultReferences[0].Location).FullName, "Microsoft.Win32.Registry.dll"));
+            var stdLibPath = Directory.GetParent(DefaultReferences[0].Location).FullName;
+            references.Add(Path.Combine(stdLibPath, "System.dll"));
+            references.Add(Path.Combine(stdLibPath, "System.Runtime.dll"));
+            references.Add(Path.Combine(stdLibPath, "System.Collections.dll"));
+            references.Add(Path.Combine(stdLibPath, "Microsoft.Win32.Registry.dll"));
 
             // HACK: C# will give compilation errors if a LIB variable contains non-existing directories
             Environment.SetEnvironmentVariable("LIB", null);
@@ -147,13 +153,12 @@ namespace Flax.Build
 
             // Run the compilation
             using var memoryStream = new MemoryStream();
-
+            CSharpParseOptions parseOptions = CSharpParseOptions.Default.WithLanguageVersion(LanguageVersion.CSharp11).WithPreprocessorSymbols(PreprocessorSymbols);
             var syntaxTrees = new List<SyntaxTree>();
             foreach (var sourceFile in SourceFiles)
             {
                 var stringText = SourceText.From(File.ReadAllText(sourceFile), Encoding.UTF8);
-                var parsedSyntaxTree = SyntaxFactory.ParseSyntaxTree(stringText,
-                    CSharpParseOptions.Default.WithLanguageVersion(LanguageVersion.CSharp9), sourceFile);
+                var parsedSyntaxTree = SyntaxFactory.ParseSyntaxTree(stringText, parseOptions, sourceFile);
                 syntaxTrees.Add(parsedSyntaxTree);
             }
 
diff --git a/Source/Tools/Flax.Build/Build/Builder.Rules.cs b/Source/Tools/Flax.Build/Build/Builder.Rules.cs
index d4fb9aa7f..d3e84d613 100644
--- a/Source/Tools/Flax.Build/Build/Builder.Rules.cs
+++ b/Source/Tools/Flax.Build/Build/Builder.Rules.cs
@@ -189,6 +189,7 @@ namespace Flax.Build
                 using (new ProfileEventScope("CompileRules"))
                 {
                     var assembler = new Assembler(files, Path.Combine(Globals.Root, Configuration.IntermediateFolder));
+                    EngineTarget.AddVersionDefines(assembler.PreprocessorSymbols);
                     assembly = assembler.Build();
                 }
 
diff --git a/Source/Tools/Flax.Build/Build/EngineTarget.cs b/Source/Tools/Flax.Build/Build/EngineTarget.cs
index e2fd54ae6..30e0c92f8 100644
--- a/Source/Tools/Flax.Build/Build/EngineTarget.cs
+++ b/Source/Tools/Flax.Build/Build/EngineTarget.cs
@@ -1,6 +1,7 @@
 // Copyright (c) 2012-2023 Wojciech Figat. All rights reserved.
 
 using System;
+using System.Collections.Generic;
 using System.IO;
 using Flax.Build.Graph;
 using Flax.Build.NativeCpp;
@@ -36,6 +37,19 @@ namespace Flax.Build
             }
         }
 
+        /// <summary>
+        /// Adds the version defines for the preprocessor (eg. FLAX_1_6_OR_NEWER).
+        /// </summary>
+        /// <param name="defines">Output list.</param>
+        public static void AddVersionDefines(ICollection<string> defines)
+        {
+            var engineVersion = EngineVersion;
+            defines.Add(string.Format("FLAX_{0}", engineVersion.Major));
+            defines.Add(string.Format("FLAX_{0}_{1}", engineVersion.Major, engineVersion.Minor));
+            for (int minor = 1; minor <= engineVersion.Minor; minor++)
+                defines.Add(string.Format("FLAX_{0}_{1}_OR_NEWER", engineVersion.Major, minor));
+        }
+
         /// <inheritdoc />
         public override void Init()
         {
diff --git a/Source/Tools/Flax.Build/Build/GameModule.cs b/Source/Tools/Flax.Build/Build/GameModule.cs
index 82ce9593d..42063e88e 100644
--- a/Source/Tools/Flax.Build/Build/GameModule.cs
+++ b/Source/Tools/Flax.Build/Build/GameModule.cs
@@ -24,9 +24,8 @@ namespace Flax.Build
             options.PublicDependencies.Add("Scripting");
 
             // Setup scripting API environment
-            var engineVersion = EngineTarget.EngineVersion;
-            AddEngineVersionDefines(engineVersion, options.ScriptingAPI.Defines);
-            AddEngineVersionDefines(engineVersion, options.CompileEnv.PreprocessorDefinitions);
+            EngineTarget.AddVersionDefines(options.ScriptingAPI.Defines);
+            EngineTarget.AddVersionDefines(options.CompileEnv.PreprocessorDefinitions);
             options.ScriptingAPI.Defines.Add("FLAX");
             options.ScriptingAPI.Defines.Add("FLAX_ASSERTIONS");
             if (options.Target.IsEditor)
@@ -38,14 +37,6 @@ namespace Flax.Build
                 options.ScriptingAPI.Defines.Add("FLAX_GAME");
             }
         }
-
-        private void AddEngineVersionDefines(Version engineVersion, HashSet<string> defines)
-        {
-            defines.Add(string.Format("FLAX_{0}", engineVersion.Major));
-            defines.Add(string.Format("FLAX_{0}_{1}", engineVersion.Major, engineVersion.Minor));
-            for (int minor = 1; minor <= engineVersion.Minor; minor++)
-                defines.Add(string.Format("FLAX_{0}_{1}_OR_NEWER", engineVersion.Major, minor));
-        }
     }
 
     /// <summary>