diff --git a/Source/Tools/Flax.Build/Configuration.cs b/Source/Tools/Flax.Build/Configuration.cs
index baa4e30b1..28970f289 100644
--- a/Source/Tools/Flax.Build/Configuration.cs
+++ b/Source/Tools/Flax.Build/Configuration.cs
@@ -1,5 +1,7 @@
 // Copyright (c) 2012-2021 Wojciech Figat. All rights reserved.
 
+using System.Collections.Generic;
+
 namespace Flax.Build
 {
     /// <summary>
@@ -198,5 +200,10 @@ namespace Flax.Build
         /// </summary>
         [CommandLine("customProjectFormat", "<type>", "Generates code project files for a custom project format type. Valid only with -genproject option.")]
         public static string ProjectFormatCustom = null;
+
+        /// <summary>
+        /// Custom configuration defines provided via command line for the build tool.
+        /// </summary>
+        public static List<string> CustomDefines = new List<string>();
     }
 }
diff --git a/Source/Tools/Flax.Build/Program.cs b/Source/Tools/Flax.Build/Program.cs
index fc6d86b3b..89e71ace0 100644
--- a/Source/Tools/Flax.Build/Program.cs
+++ b/Source/Tools/Flax.Build/Program.cs
@@ -32,6 +32,16 @@ namespace Flax.Build
             {
                 // Setup
                 CommandLine.Configure(typeof(Configuration));
+                foreach (var option in CommandLine.GetOptions())
+                {
+                    if (option.Name.Length > 1 && option.Name[0] == 'D')
+                    {
+                        var define = option.Name.Substring(1);
+                        if (!string.IsNullOrEmpty(option.Value))
+                            define += "=" + option.Value;
+                        Configuration.CustomDefines.Add(define);
+                    }
+                }
                 if (Configuration.CurrentDirectory != null)
                     Environment.CurrentDirectory = Configuration.CurrentDirectory;
                 Globals.Root = Directory.GetCurrentDirectory();