diff --git a/src/GitVersion.Core.Tests/Helpers/ParticipantSanitizerTests.cs b/src/GitVersion.Core.Tests/Helpers/ParticipantSanitizerTests.cs
new file mode 100644
index 0000000000..ad5f854bd3
--- /dev/null
+++ b/src/GitVersion.Core.Tests/Helpers/ParticipantSanitizerTests.cs
@@ -0,0 +1,67 @@
+using GitVersion.Testing.Helpers;
+
+namespace GitVersion.Core.Tests.Helpers;
+
+[TestFixture]
+public class ParticipantSanitizerTests
+{
+    [TestCase("feature/1234-is-id-with-something-kebab", "feature_1234_is_id_with_something_kebab")]
+    [TestCase("feature/1234-IsSomethingPascalCase", "feature_1234_IsSomethingPascalCase")]
+    [TestCase("feature/Caps-lower-something-kebab", "feature_Caps_lower_something_kebab")]
+    [TestCase("feature/Caps-lower-is-kebab", "feature_Caps_lower_is_kebab")]
+    [TestCase("kebab-folder/1234-is-id-with-something-kebab", "kebab_folder_1234_is_id_with_something_kebab")]
+    [TestCase("kebab-folder/1234-IsSomethingPascalCase", "kebab_folder_1234_IsSomethingPascalCase")]
+    [TestCase("kebab-folder/Caps-lower-something-kebab", "kebab_folder_Caps_lower_something_kebab")]
+    [TestCase("kebab-folder/Caps-lower-is-kebab", "kebab_folder_Caps_lower_is_kebab")]
+    [TestCase("PascalCaseFolder/1234-is-id-with-something-kebab", "PascalCaseFolder_1234_is_id_with_something_kebab")]
+    [TestCase("PascalCaseFolder/1234-IsSomethingPascalCase", "PascalCaseFolder_1234_IsSomethingPascalCase")]
+    [TestCase("PascalCaseFolder/Caps-lower-something-kebab", "PascalCaseFolder_Caps_lower_something_kebab")]
+    [TestCase("PascalCaseFolder/Caps-lower-is-kebab", "PascalCaseFolder_Caps_lower_is_kebab")]
+    [TestCase("1234-is-id-with-something-kebab", "1234_is_id_with_something_kebab")]
+    [TestCase("1234-IsSomethingPascalCase", "1234_IsSomethingPascalCase")]
+    [TestCase("Caps-lower-something-kebab", "Caps_lower_something_kebab")]
+    [TestCase("Caps-lower-is-kebab", "Caps_lower_is_kebab")]
+    [TestCase("feature/all-lower-is-kebab", "feature_all_lower_is_kebab")]
+    [TestCase("feature/24321-Upperjustoneword", "feature_24321_Upperjustoneword")]
+    [TestCase("feature/justoneword", "feature_justoneword")]
+    [TestCase("feature/PascalCase", "feature_PascalCase")]
+    [TestCase("feature/PascalCase-with-kebab", "feature_PascalCase_with_kebab")]
+    [TestCase("feature/12414", "feature_12414")]
+    [TestCase("feature/12414/12342-FeatureStoryTaskWithShortDescription", "feature_12414_12342_FeatureStoryTaskWithShortDescription")]
+    [TestCase("feature/12414/12342-Short-description", "feature_12414_12342_Short_description")]
+    [TestCase("feature/12414/12342-short-description", "feature_12414_12342_short_description")]
+    [TestCase("feature/12414/12342-Short-Description", "feature_12414_12342_Short_Description")]
+    [TestCase("release/1.0.0", "release_1_0_0")]
+    [TestCase("releases", "releases")]
+    [TestCase("feature", "feature")]
+    [TestCase("feature/tfs1-Short-description", "feature_tfs1_Short_description")]
+    [TestCase("feature/f2-Short-description", "feature_f2_Short_description")]
+    [TestCase("feature/bug1", "feature_bug1")]
+    [TestCase("f2", "f2")]
+    [TestCase("feature/f2", "feature_f2")]
+    [TestCase("feature/story2", "feature_story2")]
+    [TestCase("master", "master")]
+    [TestCase("develop", "develop")]
+    [TestCase("main", "main")]
+    public void SanitizeValidParticipant_ShouldReturnExpectedResult(string input, string expected)
+    {
+        var actual = ParticipantSanitizer.SanitizeParticipant(input);
+        actual.ShouldBe(expected);
+    }
+
+    [TestCase("")]
+    [TestCase(" ")]
+    public void SanitizeEmptyOrWhitespaceParticipant_ShouldThrow(string value)
+    {
+        var exception = Should.Throw<ArgumentException>(() => ParticipantSanitizer.SanitizeParticipant(value));
+        exception.Message.ShouldBe("The value cannot be an empty string or composed entirely of whitespace. (Parameter 'participant')");
+    }
+
+    [TestCase("feature/")]
+    [TestCase("/")]
+    public void SanitizeInvalidParticipant_ShouldThrow(string value)
+    {
+        var exception = Should.Throw<ArgumentException>(() => ParticipantSanitizer.SanitizeParticipant(value));
+        exception.Message.ShouldBe("The value cannot end with a folder separator ('/'). (Parameter 'participant')");
+    }
+}
diff --git a/src/GitVersion.Core/Core/RegexPatterns.cs b/src/GitVersion.Core/Core/RegexPatterns.cs
index a9ad425397..57d805fdab 100644
--- a/src/GitVersion.Core/Core/RegexPatterns.cs
+++ b/src/GitVersion.Core/Core/RegexPatterns.cs
@@ -53,6 +53,7 @@ public static Regex GetOrAdd([StringSyntax(StringSyntaxAttribute.Regex)] string
                 [Output.CsharpAssemblyAttributeRegexPattern] = Output.CsharpAssemblyAttributeRegex,
                 [Output.FsharpAssemblyAttributeRegexPattern] = Output.FsharpAssemblyAttributeRegex,
                 [Output.VisualBasicAssemblyAttributeRegexPattern] = Output.VisualBasicAssemblyAttributeRegex,
+                [Output.SanitizeParticipantRegexPattern] = Output.SanitizeParticipantRegex,
                 [VersionCalculation.DefaultMajorRegexPattern] = VersionCalculation.DefaultMajorRegex,
                 [VersionCalculation.DefaultMinorRegexPattern] = VersionCalculation.DefaultMinorRegex,
                 [VersionCalculation.DefaultPatchRegexPattern] = VersionCalculation.DefaultPatchRegex,
@@ -227,6 +228,9 @@ internal static partial class Output
         [StringSyntax(StringSyntaxAttribute.Regex)]
         internal const string VisualBasicAssemblyAttributeRegexPattern = @"(\s*\<Assembly:\s*(?:.*)\>\s*$(\r?\n)?)";
 
+        [StringSyntax(StringSyntaxAttribute.Regex)]
+        internal const string SanitizeParticipantRegexPattern = "[^a-zA-Z0-9]";
+
         [GeneratedRegex(AssemblyVersionRegexPattern, Options)]
         public static partial Regex AssemblyVersionRegex();
 
@@ -244,6 +248,9 @@ internal static partial class Output
 
         [GeneratedRegex(VisualBasicAssemblyAttributeRegexPattern, Options | RegexOptions.Multiline)]
         public static partial Regex VisualBasicAssemblyAttributeRegex();
+
+        [GeneratedRegex(SanitizeParticipantRegexPattern, Options)]
+        public static partial Regex SanitizeParticipantRegex();
     }
 
     internal static partial class VersionCalculation
diff --git a/src/GitVersion.Core/GitVersion.Core.csproj b/src/GitVersion.Core/GitVersion.Core.csproj
index bc311c70f1..0843eba8da 100644
--- a/src/GitVersion.Core/GitVersion.Core.csproj
+++ b/src/GitVersion.Core/GitVersion.Core.csproj
@@ -34,6 +34,7 @@
         <InternalsVisibleTo Include="GitVersion.Output.Tests" />
         <InternalsVisibleTo Include="GitVersion.App.Tests" />
         <InternalsVisibleTo Include="GitVersion.MsBuild.Tests" />
+        <InternalsVisibleTo Include="GitVersion.Testing" />
     </ItemGroup>
 
 </Project>
diff --git a/src/GitVersion.Testing/Fixtures/SequenceDiagram.cs b/src/GitVersion.Testing/Fixtures/SequenceDiagram.cs
index bf6a82ad86..35e73d21cf 100644
--- a/src/GitVersion.Testing/Fixtures/SequenceDiagram.cs
+++ b/src/GitVersion.Testing/Fixtures/SequenceDiagram.cs
@@ -1,3 +1,4 @@
+using GitVersion.Testing.Helpers;
 using GitVersion.Testing.Internal;
 
 namespace GitVersion.Testing;
@@ -39,11 +40,12 @@ public SequenceDiagram()
     /// </summary>
     public void Participant(string participant, string? @as = null)
     {
-        this.participants.Add(participant, @as ?? participant);
-        if (@as == null)
+        var cleanParticipant = ParticipantSanitizer.SanitizeParticipant(@as ?? participant);
+        this.participants.Add(participant, cleanParticipant);
+        if (participant == cleanParticipant)
             this.diagramBuilder.AppendLineFormat("participant {0}", participant);
         else
-            this.diagramBuilder.AppendLineFormat("participant \"{0}\" as {1}", participant, @as);
+            this.diagramBuilder.AppendLineFormat("participant \"{0}\" as {1}", participant, cleanParticipant);
     }
 
     /// <summary>
diff --git a/src/GitVersion.Testing/GitVersion.Testing.csproj b/src/GitVersion.Testing/GitVersion.Testing.csproj
index 97b286db82..08c0eba912 100644
--- a/src/GitVersion.Testing/GitVersion.Testing.csproj
+++ b/src/GitVersion.Testing/GitVersion.Testing.csproj
@@ -8,9 +8,6 @@
         <PackageReference Include="System.IO.Abstractions" />
         <PackageReference Include="System.Reflection.Metadata" />
     </ItemGroup>
-    <ItemGroup>
-        <Compile Include="..\GitVersion.Core\Helpers\FileSystemHelper.cs" Link="Helpers\FileSystemHelper.cs" />
-    </ItemGroup>
     <ItemGroup>
         <InternalsVisibleTo Include="GitVersion.BuildAgents.Tests" />
         <InternalsVisibleTo Include="GitVersion.Configuration.Tests" />
@@ -19,4 +16,7 @@
         <InternalsVisibleTo Include="GitVersion.App.Tests" />
         <InternalsVisibleTo Include="GitVersion.MsBuild.Tests" />
     </ItemGroup>
+    <ItemGroup>
+      <ProjectReference Include="..\GitVersion.Core\GitVersion.Core.csproj" />
+    </ItemGroup>
 </Project>
diff --git a/src/GitVersion.Testing/Helpers/ParticipantSanitizer.cs b/src/GitVersion.Testing/Helpers/ParticipantSanitizer.cs
new file mode 100644
index 0000000000..826728b19b
--- /dev/null
+++ b/src/GitVersion.Testing/Helpers/ParticipantSanitizer.cs
@@ -0,0 +1,26 @@
+using GitVersion.Core;
+
+namespace GitVersion.Testing.Helpers;
+
+public static class ParticipantSanitizer
+{
+    /// <summary>
+    /// Converts a participant identifier to a standardized format that won't break PlantUml.
+    /// </summary>
+    /// <param name="participant">The participant identifier to convert. This value cannot be null, empty, or consist only of whitespace.</param>
+    public static string SanitizeParticipant(string participant)
+    {
+        GuardAgainstInvalidParticipants(participant);
+
+        return RegexPatterns.Output.SanitizeParticipantRegex().Replace(participant, "_");
+    }
+
+    private static void GuardAgainstInvalidParticipants(string participant)
+    {
+        ArgumentException.ThrowIfNullOrWhiteSpace(participant);
+        if (participant.EndsWith('/'))
+        {
+            throw new ArgumentException("The value cannot end with a folder separator ('/').", nameof(participant));
+        }
+    }
+}