diff --git a/Gu.Roslyn.Asserts.Tests/RoslynAssertTests/Diagnostics.Fail.cs b/Gu.Roslyn.Asserts.Tests/RoslynAssertTests/Diagnostics.Fail.cs
index 42d353b9..3c25e3ee 100644
--- a/Gu.Roslyn.Asserts.Tests/RoslynAssertTests/Diagnostics.Fail.cs
+++ b/Gu.Roslyn.Asserts.Tests/RoslynAssertTests/Diagnostics.Fail.cs
@@ -538,15 +538,6 @@ public static void WhenMoreThanOne()
                 Assert.AreEqual(expected, exception.Message);
             }
 
-            [Test]
-            public static void DuplicateId()
-            {
-                var expected = "SyntaxNodeAnalyzer.SupportedDiagnostics has more than one descriptor with ID 'ID1'.";
-                var analyzer = new SyntaxNodeAnalyzer(Descriptors.Id1, Descriptors.Id1Duplicate);
-                var exception = Assert.Throws<AssertException>(() => RoslynAssert.Diagnostics(analyzer, ExpectedDiagnostic.Create(Descriptors.Id1), string.Empty));
-                Assert.AreEqual(expected, exception.Message);
-            }
-
             [Test]
             public static void SingleDocumentTwoErrors()
             {
diff --git a/Gu.Roslyn.Asserts.Tests/RoslynAssertTests/FixAll.Fail.cs b/Gu.Roslyn.Asserts.Tests/RoslynAssertTests/FixAll.Fail.cs
index bcae6c53..7db9faa1 100644
--- a/Gu.Roslyn.Asserts.Tests/RoslynAssertTests/FixAll.Fail.cs
+++ b/Gu.Roslyn.Asserts.Tests/RoslynAssertTests/FixAll.Fail.cs
@@ -425,17 +425,6 @@ class C
 ";
                 CodeAssert.AreEqual(expected, exception.Message);
             }
-
-            [Test]
-            public static void DuplicateId()
-            {
-                var expected = "SyntaxNodeAnalyzer.SupportedDiagnostics has more than one descriptor with ID 'ID1'.";
-                var analyzer = new SyntaxNodeAnalyzer(Descriptors.Id1, Descriptors.Id1Duplicate);
-                var fix = new DuplicateIdFix();
-                var expectedDiagnostic = ExpectedDiagnostic.Create(Descriptors.Id1);
-                var exception = Assert.Throws<AssertException>(() => RoslynAssert.FixAll(analyzer, fix, expectedDiagnostic, string.Empty, string.Empty));
-                Assert.AreEqual(expected, exception.Message);
-            }
         }
     }
 }
diff --git a/Gu.Roslyn.Asserts.Tests/RoslynAssertTests/NoFix.Fail.cs b/Gu.Roslyn.Asserts.Tests/RoslynAssertTests/NoFix.Fail.cs
index e50f3768..a294eda3 100644
--- a/Gu.Roslyn.Asserts.Tests/RoslynAssertTests/NoFix.Fail.cs
+++ b/Gu.Roslyn.Asserts.Tests/RoslynAssertTests/NoFix.Fail.cs
@@ -119,17 +119,6 @@ class C2
                 CodeAssert.AreEqual(expected, exception.Message);
             }
 
-            [Test]
-            public static void DuplicateId()
-            {
-                var expected = "SyntaxNodeAnalyzer.SupportedDiagnostics has more than one descriptor with ID 'ID1'.";
-                var analyzer = new SyntaxNodeAnalyzer(Descriptors.Id1, Descriptors.Id1Duplicate);
-                var fix = new DuplicateIdFix();
-                var expectedDiagnostic = ExpectedDiagnostic.Create(Descriptors.Id1);
-                var exception = Assert.Throws<AssertException>(() => RoslynAssert.NoFix(analyzer, fix, expectedDiagnostic, string.Empty));
-                Assert.AreEqual(expected, exception.Message);
-            }
-
             [Test]
             public static void WhenNoAnalyzerDiagnosticsButCompilerError()
             {
diff --git a/Gu.Roslyn.Asserts.Tests/RoslynAssertTests/Valid.Fail.cs b/Gu.Roslyn.Asserts.Tests/RoslynAssertTests/Valid.Fail.cs
index 55c4e7be..f504f99c 100644
--- a/Gu.Roslyn.Asserts.Tests/RoslynAssertTests/Valid.Fail.cs
+++ b/Gu.Roslyn.Asserts.Tests/RoslynAssertTests/Valid.Fail.cs
@@ -274,16 +274,6 @@ class C
                 Assert.AreEqual(expected, exception.Message);
             }
 
-            [Test]
-            public static void DuplicateId()
-            {
-                var expected = "SyntaxNodeAnalyzer.SupportedDiagnostics has more than one descriptor with ID 'ID1'.";
-                var analyzer = new SyntaxNodeAnalyzer(Descriptors.Id1, Descriptors.Id1Duplicate);
-                var descriptor = Descriptors.Id1;
-                var exception = Assert.Throws<AssertException>(() => RoslynAssert.Valid(analyzer, descriptor, string.Empty));
-                Assert.AreEqual(expected, exception.Message);
-            }
-
             [Test]
             public static void WhenCompilerWarnings()
             {
diff --git a/Gu.Roslyn.Asserts.Tests/TestHelpers/CodeFixes/DuplicateIdFix.cs b/Gu.Roslyn.Asserts.Tests/TestHelpers/CodeFixes/DuplicateIdFix.cs
deleted file mode 100644
index 511ac1b6..00000000
--- a/Gu.Roslyn.Asserts.Tests/TestHelpers/CodeFixes/DuplicateIdFix.cs
+++ /dev/null
@@ -1,18 +0,0 @@
-namespace Gu.Roslyn.Asserts.Tests.CodeFixes
-{
-    using System;
-    using System.Collections.Immutable;
-    using System.Threading.Tasks;
-    using Microsoft.CodeAnalysis;
-    using Microsoft.CodeAnalysis.CodeFixes;
-
-    [ExportCodeFixProvider(LanguageNames.CSharp, Name = nameof(DuplicateIdFix))]
-    internal class DuplicateIdFix : CodeFixProvider
-    {
-        public override ImmutableArray<string> FixableDiagnosticIds { get; } = ImmutableArray.Create(Descriptors.Id1.Id);
-
-        public override FixAllProvider GetFixAllProvider() => WellKnownFixAllProviders.BatchFixer;
-
-        public override Task RegisterCodeFixesAsync(CodeFixContext context) => throw new NotSupportedException();
-    }
-}
diff --git a/Gu.Roslyn.Asserts/RoslynAssert.cs b/Gu.Roslyn.Asserts/RoslynAssert.cs
index 717bc68a..72f5d613 100644
--- a/Gu.Roslyn.Asserts/RoslynAssert.cs
+++ b/Gu.Roslyn.Asserts/RoslynAssert.cs
@@ -158,29 +158,13 @@ internal static void VerifySingleSupportedSuppression(DiagnosticSuppressor suppr
         /// <param name="expectedId">The descriptor of the supported diagnostic.</param>
         internal static void VerifyAnalyzerSupportsDiagnostic(DiagnosticAnalyzer analyzer, string expectedId)
         {
-            if (analyzer.SupportedDiagnostics.Length > 0 &&
-                analyzer.SupportedDiagnostics.Length != analyzer.SupportedDiagnostics.Select(x => x.Id).Distinct().Count())
-            {
-                var message = $"{analyzer.GetType().Name}.SupportedDiagnostics has more than one descriptor with ID '{analyzer.SupportedDiagnostics.ToLookup(x => x.Id).First(x => x.Count() > 1).Key}'.";
-                throw new AssertException(message);
-            }
-
-            var descriptors = analyzer.SupportedDiagnostics.Count(x => x.Id == expectedId);
-            if (descriptors == 0)
+            if (!analyzer.SupportedDiagnostics.Any(x => x.Id == expectedId))
             {
                 var message = $"{analyzer.GetType().Name} does not produce a diagnostic with ID '{expectedId}'.{Environment.NewLine}" +
                               $"{analyzer.GetType().Name}.{nameof(analyzer.SupportedDiagnostics)}: {Format(analyzer.SupportedDiagnostics)}.{Environment.NewLine}" +
                               $"The expected diagnostic is: '{expectedId}'.";
                 throw new AssertException(message);
             }
-
-            if (descriptors > 1)
-            {
-                var message = $"{analyzer.GetType().Name} supports multiple diagnostics with ID '{expectedId}'.{Environment.NewLine}" +
-                              $"{analyzer.GetType().Name}.{nameof(analyzer.SupportedDiagnostics)}: {Format(analyzer.SupportedDiagnostics)}.{Environment.NewLine}" +
-                              $"The expected diagnostic is: {expectedId}.";
-                throw new AssertException(message);
-            }
         }
 
         /// <summary>