diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 3a63125..00cf88a 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -6,12 +6,10 @@ on:
     branches:
       - main
       - feature/*
+      - hotfix/*
     tags:
       - "[0-9]+.[0-9]+.[0-9]+"
       - "[0-9]+.[0-9]+.[0-9]+-**"
-  pull_request:
-    branches:
-      - main
 
 jobs:
   test:
diff --git a/src/AutoCtor.Shared/AttributeSourceGenerator/Emitter.cs b/src/AutoCtor.Shared/AttributeSourceGenerator/Emitter.cs
index 016a2f5..294f975 100644
--- a/src/AutoCtor.Shared/AttributeSourceGenerator/Emitter.cs
+++ b/src/AutoCtor.Shared/AttributeSourceGenerator/Emitter.cs
@@ -18,7 +18,7 @@ public static SourceText GenerateSource()
             using (source.StartBlock("namespace AutoCtor"))
             {
                 source.AddCompilerGeneratedAttribute().AddGeneratedCodeAttribute();
-                using (source.StartBlock("public enum GuardSetting"))
+                using (source.StartBlock("internal enum GuardSetting"))
                 {
                     source.AppendLine("Default,");
                     source.AppendLine("Disabled,");
diff --git a/src/AutoCtor.Tests/GeneratedAttributeTests.AttributeGeneratedCode#AutoConstructAttribute.g.verified.cs b/src/AutoCtor.Tests/GeneratedAttributeTests.AttributeGeneratedCode#AutoConstructAttribute.g.verified.cs
index a15f4a3..3d65940 100644
--- a/src/AutoCtor.Tests/GeneratedAttributeTests.AttributeGeneratedCode#AutoConstructAttribute.g.verified.cs
+++ b/src/AutoCtor.Tests/GeneratedAttributeTests.AttributeGeneratedCode#AutoConstructAttribute.g.verified.cs
@@ -9,7 +9,7 @@
 namespace AutoCtor
 {
 	[global::System.Runtime.CompilerServices.CompilerGeneratedAttribute]
-	public enum GuardSetting
+	internal enum GuardSetting
 	{
 		Default,
 		Disabled,
diff --git a/src/AutoCtor.Tests/GeneratedAttributeTests.cs b/src/AutoCtor.Tests/GeneratedAttributeTests.cs
index 35badc7..9e7be95 100644
--- a/src/AutoCtor.Tests/GeneratedAttributeTests.cs
+++ b/src/AutoCtor.Tests/GeneratedAttributeTests.cs
@@ -51,4 +51,31 @@ public async Task PreserveAttributesTest()
         Assert.Empty(diagnostics);
         Assert.Empty(outputCompilation.GetDiagnostics());
     }
+
+    [Fact]
+    public async Task EnsureGeneratedAttributesAreNotExternallyVisible()
+    {
+        // Issue 312
+        var compileBuilder = new CompilationBuilder()
+            .AddNetCoreReference()
+            .WithPreprocessorSymbols(["AUTOCTOR_EMBED_ATTRIBUTES"]);
+
+        var genDriver = new GeneratorDriverBuilder()
+            .AddGenerator(new AttributeSourceGenerator())
+            .Build(compileBuilder.ParseOptions);
+
+        var projectA = await compileBuilder
+            .Build("ProjectA");
+
+        genDriver = genDriver.RunGeneratorsAndUpdateCompilation(projectA, out var genProjectA, out _);
+
+        var projectB = await compileBuilder
+            .AddCompilationReference(genProjectA)
+            .Build("ProjectB");
+
+        genDriver.RunGeneratorsAndUpdateCompilation(projectB, out var outputCompilation, out var diagnostics);
+
+        Assert.Empty(diagnostics);
+        Assert.Empty(outputCompilation.GetDiagnostics());
+    }
 }
diff --git a/src/AutoCtor.Tests/Utilities/CompilationBuilder.cs b/src/AutoCtor.Tests/Utilities/CompilationBuilder.cs
index 25bd290..85ab6b5 100644
--- a/src/AutoCtor.Tests/Utilities/CompilationBuilder.cs
+++ b/src/AutoCtor.Tests/Utilities/CompilationBuilder.cs
@@ -78,7 +78,7 @@ public CompilationBuilder AddAssemblyReference<T>()
         };
     }
 
-    public CompilationBuilder AddCompilationReference(CSharpCompilation compilation)
+    public CompilationBuilder AddCompilationReference(Compilation compilation)
     {
         return new(this)
         {