diff --git a/src/Framework/AspNetCoreAnalyzers/test/Infrastructure/WellKnownTypesTests.cs b/src/Framework/AspNetCoreAnalyzers/test/Infrastructure/WellKnownTypesTests.cs
index 8c02e10752d8..7619fa767fd1 100644
--- a/src/Framework/AspNetCoreAnalyzers/test/Infrastructure/WellKnownTypesTests.cs
+++ b/src/Framework/AspNetCoreAnalyzers/test/Infrastructure/WellKnownTypesTests.cs
@@ -4,7 +4,9 @@
 using System.Collections.Immutable;
 using Microsoft.AspNetCore.Analyzer.Testing;
 using Microsoft.AspNetCore.App.Analyzers.Infrastructure;
+using Microsoft.AspNetCore.Razor.Hosting;
 using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp;
 using Microsoft.CodeAnalysis.Diagnostics;
 
 namespace Microsoft.AspNetCore.Analyzers.Infrastructure;
@@ -34,6 +36,52 @@ static void Main()
         Assert.Collection(diagnostics, d => Assert.Equal("TEST001", d.Id));
     }
 
+    [Theory]
+    [InlineData("ExternAssembly")]
+    [InlineData("SystemFoo")]
+    [InlineData("MicrosoftFoo")]
+    public async Task ResolveAllWellKnownTypes_ToleratesDuplicateTypeNames(string assemblyName)
+    {
+        // Arrange
+        var source = TestSource.Read(@"
+class Program
+{
+    static void Main()
+    {
+    }
+}
+");
+        var referenceSource = """
+  namespace Microsoft.AspNetCore.Builder
+  {
+      public static class EndpointRouteBuilderExtensions
+      {
+      }
+  }
+  """;
+        // Act
+        var project = TestDiagnosticAnalyzerRunner.CreateProjectWithReferencesInBinDir(GetType().Assembly, source.Source);
+        Stream assemblyStream = GetInMemoryAssemblyStreamForCode(referenceSource, assemblyName, project.MetadataReferences.ToArray());
+        project = project.AddMetadataReference(MetadataReference.CreateFromStream(assemblyStream));
+        var diagnostics = await Runner.GetDiagnosticsAsync(project);
+
+        // Assert
+        Assert.Collection(diagnostics, d => Assert.Equal("TEST001", d.Id));
+    }
+
+    private static Stream GetInMemoryAssemblyStreamForCode(string code, string assemblyName, params MetadataReference[] references)
+    {
+        var tree = CSharpSyntaxTree.ParseText(code);
+        var trees = ImmutableArray.Create(tree);
+        var options = new CSharpCompilationOptions(OutputKind.DynamicallyLinkedLibrary);
+        var compilation = CSharpCompilation.Create(assemblyName, trees).WithOptions(options);
+        compilation = compilation.AddReferences(references);
+        var stream = new MemoryStream();
+        var emitResult = compilation.Emit(stream);
+        stream.Seek(0, SeekOrigin.Begin);
+        return stream;
+    }
+
     [DiagnosticAnalyzer(LanguageNames.CSharp)]
     private class TestAnalyzer : DiagnosticAnalyzer
     {
diff --git a/src/Shared/RoslynUtils/WellKnownTypes.cs b/src/Shared/RoslynUtils/WellKnownTypes.cs
index 27e44a583cbc..a3a5cd3061b7 100644
--- a/src/Shared/RoslynUtils/WellKnownTypes.cs
+++ b/src/Shared/RoslynUtils/WellKnownTypes.cs
@@ -74,7 +74,7 @@ public INamedTypeSymbol Get(WellKnownTypeData.WellKnownType type)
 
     private INamedTypeSymbol GetAndCache(int index)
     {
-        var result = _compilation.GetTypeByMetadataName(WellKnownTypeData.WellKnownTypeNames[index]);
+        var result = GetTypeByMetadataNameInTargetAssembly(WellKnownTypeData.WellKnownTypeNames[index]);
         if (result == null)
         {
             throw new InvalidOperationException($"Failed to resolve well-known type '{WellKnownTypeData.WellKnownTypeNames[index]}'.");
@@ -86,6 +86,33 @@ private INamedTypeSymbol GetAndCache(int index)
         return _lazyWellKnownTypes[index]!;
     }
 
+    // Filter for types within well-known (framework-owned) assemblies only.
+    private INamedTypeSymbol? GetTypeByMetadataNameInTargetAssembly(string metadataName)
+    {
+        var types = _compilation.GetTypesByMetadataName(metadataName);
+        if (types.Length == 0)
+        {
+            return null;
+        }
+
+        if (types.Length == 1)
+        {
+            return types[0];
+        }
+
+        // Multiple types match the name. This is most likely caused by someone reusing the namespace + type name in their apps or libraries.
+        // Workaround this situation by prioritizing types in System and Microsoft assemblies.
+        foreach (var type in types)
+        {
+            if (type.ContainingAssembly.Identity.Name.StartsWith("System.", StringComparison.Ordinal)
+                || type.ContainingAssembly.Identity.Name.StartsWith("Microsoft.", StringComparison.Ordinal))
+            {
+                return type;
+            }
+        }
+        return null;
+    }
+
     public bool IsType(ITypeSymbol type, WellKnownTypeData.WellKnownType[] wellKnownTypes) => IsType(type, wellKnownTypes, out var _);
 
     public bool IsType(ITypeSymbol type, WellKnownTypeData.WellKnownType[] wellKnownTypes, [NotNullWhen(true)] out WellKnownTypeData.WellKnownType? match)