diff --git a/src/StreamJsonRpc/SkipClrVisibilityChecks.cs b/src/StreamJsonRpc/SkipClrVisibilityChecks.cs
index 273ba0ba..a1c1e013 100644
--- a/src/StreamJsonRpc/SkipClrVisibilityChecks.cs
+++ b/src/StreamJsonRpc/SkipClrVisibilityChecks.cs
@@ -87,12 +87,15 @@ internal static ImmutableHashSet<AssemblyName> GetSkipVisibilityChecksRequiremen
             CheckForNonPublicTypes(typeInfo, assembliesDeclaringInternalTypes, visitedTypes);
 
             // Enumerate members on the interface that we're going to need to implement.
-            foreach (MethodInfo methodInfo in typeInfo.GetMethods(BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.FlattenHierarchy))
+            foreach (TypeInfo iteratedTypeInfo in ThisAndBaseTypes(typeInfo))
             {
-                CheckForNonPublicTypes(methodInfo.ReturnType.GetTypeInfo(), assembliesDeclaringInternalTypes, visitedTypes);
-                foreach (ParameterInfo parameter in methodInfo.GetParameters())
+                foreach (MethodInfo methodInfo in iteratedTypeInfo.GetMethods(BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance))
                 {
-                    CheckForNonPublicTypes(parameter.ParameterType.GetTypeInfo(), assembliesDeclaringInternalTypes, visitedTypes);
+                    CheckForNonPublicTypes(methodInfo.ReturnType.GetTypeInfo(), assembliesDeclaringInternalTypes, visitedTypes);
+                    foreach (ParameterInfo parameter in methodInfo.GetParameters())
+                    {
+                        CheckForNonPublicTypes(parameter.ParameterType.GetTypeInfo(), assembliesDeclaringInternalTypes, visitedTypes);
+                    }
                 }
             }
 
@@ -131,6 +134,25 @@ internal void SkipVisibilityChecksFor(AssemblyName assemblyName)
             }
         }
 
+        private static IEnumerable<TypeInfo> ThisAndBaseTypes(TypeInfo startingPoint)
+        {
+            if (startingPoint.IsInterface)
+            {
+                yield return startingPoint.GetTypeInfo();
+                foreach (Type iface in startingPoint.GetInterfaces())
+                {
+                    yield return iface.GetTypeInfo();
+                }
+            }
+            else
+            {
+                for (TypeInfo? t = startingPoint.GetTypeInfo(); t is not null && t != typeof(object).GetTypeInfo(); t = t.BaseType?.GetTypeInfo())
+                {
+                    yield return t;
+                }
+            }
+        }
+
         private static void CheckForNonPublicTypes(TypeInfo typeInfo, ImmutableHashSet<AssemblyName>.Builder assembliesDeclaringInternalTypes, HashSet<TypeInfo> visitedTypes)
         {
             Requires.NotNull(typeInfo, nameof(typeInfo));
diff --git a/test/StreamJsonRpc.Tests.ExternalAssembly/IInternalGenericInterface.cs b/test/StreamJsonRpc.Tests.ExternalAssembly/IInternalGenericInterface.cs
new file mode 100644
index 00000000..810c2285
--- /dev/null
+++ b/test/StreamJsonRpc.Tests.ExternalAssembly/IInternalGenericInterface.cs
@@ -0,0 +1,12 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+namespace StreamJsonRpc.Tests.ExternalAssembly
+{
+    using System.Threading.Tasks;
+
+    internal interface IInternalGenericInterface<TOptions>
+    {
+        Task<TOptions> GetOptionsAsync(InternalStruct id, CancellationToken cancellationToken);
+    }
+}
diff --git a/test/StreamJsonRpc.Tests.ExternalAssembly/InternalStruct.cs b/test/StreamJsonRpc.Tests.ExternalAssembly/InternalStruct.cs
new file mode 100644
index 00000000..7c12e43d
--- /dev/null
+++ b/test/StreamJsonRpc.Tests.ExternalAssembly/InternalStruct.cs
@@ -0,0 +1,9 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+namespace StreamJsonRpc.Tests.ExternalAssembly
+{
+    internal struct InternalStruct
+    {
+    }
+}
diff --git a/test/StreamJsonRpc.Tests/JsonRpcProxyGenerationTests.cs b/test/StreamJsonRpc.Tests/JsonRpcProxyGenerationTests.cs
index 1126ae06..cf790795 100644
--- a/test/StreamJsonRpc.Tests/JsonRpcProxyGenerationTests.cs
+++ b/test/StreamJsonRpc.Tests/JsonRpcProxyGenerationTests.cs
@@ -1,16 +1,13 @@
 // Copyright (c) Microsoft Corporation. All rights reserved.
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
-using System;
-using System.IO;
-using System.Threading;
-using System.Threading.Tasks;
 using Microsoft;
 using Microsoft.VisualStudio.Threading;
 using Nerdbank;
 using StreamJsonRpc;
 using Xunit;
 using Xunit.Abstractions;
+using ExAssembly = StreamJsonRpc.Tests.ExternalAssembly;
 
 public class JsonRpcProxyGenerationTests : TestBase
 {
@@ -137,14 +134,27 @@ public interface IServerWithGenericMethod
         Task AddAsync<T>(T a, T b);
     }
 
-    internal interface IServerInternal : StreamJsonRpc.Tests.ExternalAssembly.ISomeInternalProxyInterface, IServerInternalWithInternalTypesFromOtherAssemblies
+    internal interface IServerInternal : ExAssembly.ISomeInternalProxyInterface, IServerInternalWithInternalTypesFromOtherAssemblies
     {
         Task<int> AddAsync(int a, int b);
     }
 
     internal interface IServerInternalWithInternalTypesFromOtherAssemblies
     {
-        Task<StreamJsonRpc.Tests.ExternalAssembly.SomeOtherInternalType> SomeMethodAsync();
+        Task<ExAssembly.SomeOtherInternalType> SomeMethodAsync();
+    }
+
+    internal interface IRemoteService
+    {
+        internal interface ICallback : ExAssembly.IInternalGenericInterface<ExAssembly.SomeOtherInternalType?>
+        {
+        }
+    }
+
+    [Fact]
+    public void Tomas_Internal()
+    {
+        JsonRpc.Attach<IRemoteService.ICallback>(new MemoryStream());
     }
 
     [Fact]
@@ -428,7 +438,7 @@ public async Task InternalInterface()
         var clientRpc = JsonRpc.Attach(streams.Item1);
 
         // Try the first internal interface, which is external to this test assembly
-        var proxy1 = clientRpc.Attach<StreamJsonRpc.Tests.ExternalAssembly.ISomeInternalProxyInterface>();
+        var proxy1 = clientRpc.Attach<ExAssembly.ISomeInternalProxyInterface>();
         Assert.Equal(-1, await proxy1.SubtractAsync(1, 2).WithCancellation(this.TimeoutToken));
 
         // Now create a proxy for another interface that is internal within this assembly, but derives from the external assembly's internal interface.
@@ -815,11 +825,17 @@ internal class ServerOfInternalInterface : IServerInternal
     {
         public Task<int> AddAsync(int a, int b) => Task.FromResult(a + b);
 
-        public Task<StreamJsonRpc.Tests.ExternalAssembly.SomeOtherInternalType> SomeMethodAsync()
+        public Task<ExAssembly.SomeOtherInternalType> SomeMethodAsync()
         {
-            return Task.FromResult(new StreamJsonRpc.Tests.ExternalAssembly.SomeOtherInternalType());
+            return Task.FromResult(new ExAssembly.SomeOtherInternalType());
         }
 
         public Task<int> SubtractAsync(int a, int b) => Task.FromResult(a - b);
     }
+
+    internal class Callback : IRemoteService.ICallback
+    {
+        public Task<ExAssembly.SomeOtherInternalType?> GetOptionsAsync(ExAssembly.InternalStruct id, CancellationToken cancellationToken)
+            => Task.FromResult<ExAssembly.SomeOtherInternalType?>(null);
+    }
 }