diff --git a/README.md b/README.md
index 9b4928e..bdf648c 100644
--- a/README.md
+++ b/README.md
@@ -149,13 +149,13 @@ Must.BeTrue(!list.Contains(x));  // ✅ Prefer: Must.HaveSameSequence(expectedLi
 
 ## 🧭 `FUnit.Directives`
 
-With FUnit.Directives package, you can *include* external file into file-based app project by adding special directive comment `//:funit:include <path to the file>`.
+With FUnit.Directives package, you can *include* external file into file-based app project by adding special directive `#warning funit include <path to the file>`.
 
 ```cs
 #:package FUnit@*
 #:package FUnit.Directives@*
 
-//:funit:include ./path/to/external-file.cs
+#warning funit include ./path/to/external-file.cs
 
 return FUnit.Run( /* tests depending on 'external-file.cs */ );
 ```
diff --git a/directives/FUnitSourceGenerator.cs b/directives/FUnitSourceGenerator.cs
index 322b9a0..aab5702 100644
--- a/directives/FUnitSourceGenerator.cs
+++ b/directives/FUnitSourceGenerator.cs
@@ -57,12 +57,12 @@ public void Execute(GeneratorExecutionContext context)
             foreach (var syntaxTree in context.Compilation.SyntaxTrees)
             {
                 var root = syntaxTree.GetCompilationUnitRoot();
-                var comments = root
+                var directives = root
                     .DescendantTrivia()
-                    .Where(t => t.IsKind(SyntaxKind.SingleLineCommentTrivia))
+                    .Where(t => t.IsKind(SyntaxKind.WarningDirectiveTrivia))
                     .ToList();  // ToList is better than ToImmutableList in this case
 
-                foreach (var trivia in comments)
+                foreach (var trivia in directives)
                 {
                     if (trivia.SyntaxTree is null)
                     {
@@ -72,26 +72,32 @@ public void Execute(GeneratorExecutionContext context)
                         continue;
                     }
 
-                    if (!trivia.ToString().StartsWith(SR.DirectivePrefix, StringComparison.Ordinal))
+                    // Check for no indentation
+                    var line = trivia.GetLocation().GetLineSpan().StartLinePosition.Character;
+                    if (line != 0)
                     {
                         continue;
                     }
 
-                    // Check for no indentation
-                    var line = trivia.GetLocation().GetLineSpan().StartLinePosition.Character;
-                    if (line != 0)
+                    var fullText = trivia.ToString();
+                    if (!fullText.StartsWith("#warning", StringComparison.Ordinal))
                     {
                         continue;
                     }
 
-                    var fullText = trivia.ToString().TrimEnd();
+                    // 8 is the length of "#warning"
+                    var textAfterWarning = fullText.Substring(8).TrimStart();
+                    if (!textAfterWarning.StartsWith(SR.DirectivePrefix, StringComparison.Ordinal))
+                    {
+                        continue;
+                    }
 
 #if DEBUG
                     context.ReportDiagnostic(
-                        Diagnostic.Create(SR.DebugDiagnostic, trivia.GetLocation(), fullText));
+                        Diagnostic.Create(SR.DebugDiagnostic, trivia.GetLocation(), fullText.TrimEnd()));
 #endif
 
-                    var keywordAndArgs = fullText.Substring(SR.DirectivePrefix.Length);
+                    var keywordAndArgs = textAfterWarning.Substring(SR.DirectivePrefix.Length);
 
                     var parts = keywordAndArgs.Split(SR.DirectiveSeparators, 2, StringSplitOptions.RemoveEmptyEntries);
                     var keyword = parts.FirstOrDefault()?.Trim() ?? string.Empty;
diff --git a/directives/SR.cs b/directives/SR.cs
index 3f21f25..b009535 100644
--- a/directives/SR.cs
+++ b/directives/SR.cs
@@ -9,10 +9,10 @@ namespace FUnit.Directives
 {
     internal class SR
     {
-        public const string DirectivePrefix = "//:funit:";
+        public const string DirectivePrefix = "funit";
         public const string DiagnosticCategory = nameof(FUnit);
 
-        public static readonly char[] DirectiveSeparators = new[] { ' ' };
+        public static readonly char[] DirectiveSeparators = new[] { ' ', '\t' };
         public static readonly char[] InvalidChars = new[] { '/', '\\', ':' };  // File.Exists will reject invalid path so remove only directory separators
 
         public static DiagnosticDescriptor MissingFileNameDiagnostic = new(
diff --git a/sandbox/Sandbox.cs b/sandbox/Sandbox.cs
index 8e7542f..e4debac 100644
--- a/sandbox/Sandbox.cs
+++ b/sandbox/Sandbox.cs
@@ -13,28 +13,28 @@
 /* uncomment to test FUnit.Directives
 
 // multiple include of same file should be allowed
-//:funit:include Sandbox.cs
-//:funit:include Sandbox.cs  
-//:funit:include ./Sandbox.cs
-//:funit:include ./Sandbox.cs  
-
-// IGNORED: prefix must be single line comment and placed at line beginning
-//   //:funit:
-///:funit:
+#warning funit include Sandbox.cs
+#warning funit include Sandbox.cs  
+#warning funit include ./Sandbox.cs
+#warning funit include ./Sandbox.cs  
+
+// IGNORED: prefix must be #warning funit and placed at line beginning
+//   #warning funit
+//#warning funit
 // leading space is not allowed
-    //:funit:
+    #warning funit
 
 // ERRORS
-//:funit:include 
-//:funit:include  NotFound.cs
-//:funit:unknown
-//:funit: 
-//:funit:include  file not supported
+#warning funit include 
+#warning funit include  NotFound.cs
+#warning funit unknown
+#warning funit 
+#warning funit include  file not supported
 
 */
 
 
 // IGNORED: in multiline comment
 /*
-//:funit:
+#warning funit
 */
diff --git a/test/Directives_test.cs b/test/Directives_test.cs
index 7682053..dacb849 100644
--- a/test/Directives_test.cs
+++ b/test/Directives_test.cs
@@ -1,15 +1,19 @@
 #:project ../src
 #:package FUnit.Directives@*
 
+#if true
+return 0;
+#else
+
 // cannot...? --> #:project ../directives
 
 // [TEST] allow multiple include directives scattered in project
-//:funit:include Directives_TestClass.cs
-//:funit:include Directives_TestClass.cs
+#warning funit include Directives_TestClass.cs
+#warning funit include Directives_TestClass.cs
 
 // [TEST] no duplicate even if same file is specified in different way
-//:funit:include ./Directives_TestClass.cs
-//:funit:include ./Directives_TestClass.cs
+#warning funit include ./Directives_TestClass.cs
+#warning funit include ./Directives_TestClass.cs
 
 #warning THIS WARNING IS EMITTED BY PREPROCESSOR DIRECTIVE
 
@@ -17,9 +21,11 @@
 {
     describe("FUnit.Directives", it =>
     {
-        it("should work (:funit:include)", () =>
+        it("should work (#warning funit include)", () =>
         {
             Must.BeEqual(310, Tests.TestClass.TestMethod());
         });
     });
 });
+
+#endif