diff --git a/ICSharpCode.BamlDecompiler/BamlDecompilerTypeSystem.cs b/ICSharpCode.BamlDecompiler/BamlDecompilerTypeSystem.cs
index 79542334a..dd1624968 100644
--- a/ICSharpCode.BamlDecompiler/BamlDecompilerTypeSystem.cs
+++ b/ICSharpCode.BamlDecompiler/BamlDecompilerTypeSystem.cs
@@ -126,6 +126,15 @@ namespace ICSharpCode.BamlDecompiler
 				if (asm != null)
 				{
 					referencedAssemblies.Add(asm);
+					// Whether an element is a markup extension is decided by walking its base types,
+					// and a base type can sit in an assembly the document's own assembly never names.
+					// Stopping at the assemblies it does name leaves such a type unresolved, the
+					// extension unrecognised, and the decompiler's placeholder namespace in the XAML
+					// (issue #2930).
+					foreach (var indirectReference in asm.AssemblyReferences)
+					{
+						assemblyReferenceQueue.Enqueue((true, asm, indirectReference));
+					}
 					var metadata = asm.Metadata;
 					foreach (var h in metadata.ExportedTypes)
 					{
diff --git a/ILSpy.BamlDecompiler.Tests/ILSpy.BamlDecompiler.Tests.csproj b/ILSpy.BamlDecompiler.Tests/ILSpy.BamlDecompiler.Tests.csproj
index 97dde68e0..d0950e4f3 100644
--- a/ILSpy.BamlDecompiler.Tests/ILSpy.BamlDecompiler.Tests.csproj
+++ b/ILSpy.BamlDecompiler.Tests/ILSpy.BamlDecompiler.Tests.csproj
@@ -46,6 +46,7 @@
     <Compile Include="FacadeAssemblyTests.cs" />
     <Compile Include="InvalidXmlCharacterTests.cs" />
     <Compile Include="MissingReferencesTests.cs" />
+    <Compile Include="TransitiveReferenceTests.cs" />
     <Compile Include="MarkupExtensionQuotingTests.cs" />
     <Compile Include="RuntimeNamePropertyTests.cs" />
     <Compile Include="StartupUriTests.cs" />
diff --git a/ILSpy.BamlDecompiler.Tests/TransitiveReferenceTests.cs b/ILSpy.BamlDecompiler.Tests/TransitiveReferenceTests.cs
new file mode 100644
index 000000000..a68cf5ae8
--- /dev/null
+++ b/ILSpy.BamlDecompiler.Tests/TransitiveReferenceTests.cs
@@ -0,0 +1,111 @@
+// Copyright (c) 2026 Siegfried Pammer
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy of this
+// software and associated documentation files (the "Software"), to deal in the Software
+// without restriction, including without limitation the rights to use, copy, modify, merge,
+// publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons
+// to whom the Software is furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all copies or
+// substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
+// INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
+// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
+// FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Reflection.PortableExecutable;
+
+using ICSharpCode.BamlDecompiler;
+using ICSharpCode.Decompiler.Metadata;
+using ICSharpCode.Decompiler.TypeSystem;
+
+using NUnit.Framework;
+
+namespace ILSpy.BamlDecompiler.Tests
+{
+	/// <summary>
+	/// Deciding whether an element is a markup extension means walking its base types, and those
+	/// leave the assemblies a document's own assembly names. A base type landing in an assembly
+	/// nobody loaded resolves to nothing, the extension is not recognised, and it goes out as an
+	/// element tree carrying the decompiler's own placeholder namespace,
+	/// "https://github.com/icsharpcode/ILSpy", into the XAML (issue #2930).
+	/// </summary>
+	[TestFixture]
+	public class TransitiveReferenceTests
+	{
+		/// <summary>
+		/// ICSharpCode.BamlDecompiler stands in for a document's assembly here: it has references of
+		/// its own, and those references have references it does not name itself.
+		/// </summary>
+		static readonly string MainModulePath = Path.Combine(
+			Path.GetDirectoryName(typeof(TransitiveReferenceTests).Assembly.Location),
+			"ICSharpCode.BamlDecompiler.dll");
+
+		static PEFile Load(string path)
+		{
+			using var stream = new FileStream(path, FileMode.Open, FileAccess.Read);
+			return new PEFile(path, stream, streamOptions: PEStreamOptions.PrefetchEntireImage);
+		}
+
+		static ICompilation TypeSystemOf(PEFile file)
+		{
+			var resolver = new UniversalAssemblyResolver(file.FileName, throwOnError: false,
+				file.DetectTargetFrameworkId(), file.DetectRuntimePack());
+			return new BamlDecompilerTypeSystem(file, resolver);
+		}
+
+		/// <summary>
+		/// An assembly the main module reaches only through one of its own references. Derived from
+		/// the metadata rather than named here, so that changing what either assembly references
+		/// cannot quietly turn this test into one that proves nothing.
+		/// </summary>
+		static string IndirectlyReferencedAssembly(PEFile mainModule)
+		{
+			var direct = new HashSet<string>(mainModule.AssemblyReferences.Select(r => r.Name));
+			foreach (var reference in mainModule.AssemblyReferences)
+			{
+				if (reference.Name != "ICSharpCode.Decompiler")
+					continue;
+				using var referenced = Load(Path.Combine(
+					Path.GetDirectoryName(mainModule.FileName), reference.Name + ".dll"));
+				string indirect = referenced.AssemblyReferences
+					.Select(r => r.Name)
+					.FirstOrDefault(name => !direct.Contains(name));
+				Assert.That(indirect, Is.Not.Null,
+					"the premise of this test is gone: every assembly ICSharpCode.Decompiler "
+					+ "references is now referenced by ICSharpCode.BamlDecompiler as well");
+				return indirect;
+			}
+			Assert.Fail("ICSharpCode.BamlDecompiler no longer references ICSharpCode.Decompiler");
+			return null;
+		}
+
+		[Test]
+		public void AnAssemblyReachedOnlyThroughAReferenceIsLoaded()
+		{
+			using var mainModule = Load(MainModulePath);
+			string indirect = IndirectlyReferencedAssembly(mainModule);
+
+			var compilation = TypeSystemOf(mainModule);
+
+			Assert.That(compilation.Modules.Select(m => m.AssemblyName), Does.Contain(indirect));
+		}
+
+		[Test]
+		public void TheAssembliesTheModuleNamesItselfAreStillLoaded()
+		{
+			using var mainModule = Load(MainModulePath);
+
+			var compilation = TypeSystemOf(mainModule);
+
+			Assert.That(compilation.Modules.Select(m => m.AssemblyName),
+				Does.Contain("ICSharpCode.Decompiler"));
+		}
+	}
+}