diff --git a/capnpc-csharp.tests/Properties/Resources.Designer.cs b/capnpc-csharp.tests/Properties/Resources.Designer.cs
index 0f7df65..5148dec 100644
--- a/capnpc-csharp.tests/Properties/Resources.Designer.cs
+++ b/capnpc-csharp.tests/Properties/Resources.Designer.cs
@@ -129,5 +129,15 @@ namespace capnpc_csharp.Tests.Properties {
                 return ((byte[])(obj));
             }
         }
+        
+        /// <summary>
+        ///   Looks up a localized resource of type System.Byte[].
+        /// </summary>
+        internal static byte[] UnitTest4_capnp {
+            get {
+                object obj = ResourceManager.GetObject("UnitTest4_capnp", resourceCulture);
+                return ((byte[])(obj));
+            }
+        }
     }
 }
diff --git a/capnpc-csharp.tests/Properties/Resources.resx b/capnpc-csharp.tests/Properties/Resources.resx
index 2404b46..b4ecfef 100644
--- a/capnpc-csharp.tests/Properties/Resources.resx
+++ b/capnpc-csharp.tests/Properties/Resources.resx
@@ -139,4 +139,7 @@
   <data name="UnitTest11_capnp" type="System.Resources.ResXFileRef, System.Windows.Forms">
     <value>..\Resources\UnitTest11.capnp.bin;System.Byte[], mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</value>
   </data>
+  <data name="UnitTest4_capnp" type="System.Resources.ResXFileRef, System.Windows.Forms">
+    <value>..\Resources\UnitTest4.capnp.bin;System.Byte[], mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</value>
+  </data>
 </root>
\ No newline at end of file
diff --git a/capnpc-csharp.tests/Resources/UnitTest4.capnp.bin b/capnpc-csharp.tests/Resources/UnitTest4.capnp.bin
new file mode 100644
index 0000000..f93feb2
Binary files /dev/null and b/capnpc-csharp.tests/Resources/UnitTest4.capnp.bin differ
diff --git a/capnpc-csharp.tests/UnitTest4.capnp b/capnpc-csharp.tests/UnitTest4.capnp
new file mode 100644
index 0000000..edfb8c7
--- /dev/null
+++ b/capnpc-csharp.tests/UnitTest4.capnp
@@ -0,0 +1,16 @@
+@0xf463d204f5208b43;
+$import "/capnp/c++.capnp".namespace("UnitTest4");
+
+interface Node {
+	getInfo @0 () -> Info;
+}
+
+struct Info {
+	node @0 :Node;
+	classes @1 :Classes;
+}
+
+struct Classes {
+	i1 @0 :import "UnitTest4b.capnp".I1.Classes;
+	i2 @1: Void;
+}
\ No newline at end of file
diff --git a/capnpc-csharp.tests/UnitTest4b.capnp b/capnpc-csharp.tests/UnitTest4b.capnp
new file mode 100644
index 0000000..3bfe83a
--- /dev/null
+++ b/capnpc-csharp.tests/UnitTest4b.capnp
@@ -0,0 +1,15 @@
+@0x8151238e9f9884c8;
+$import "/capnp/c++.capnp".namespace("UnitTest4");
+
+using Base = import "UnitTest4.capnp";
+
+interface I1 {
+	interface Node extends (Base.Node) {}
+	struct Classes {
+		sub @0: Sub;
+	}
+	struct Sub {
+		const prototype :Base.Classes = ( i1 = (sub = ()) );
+		data @0: Bool;
+	}
+}
diff --git a/capnpc-csharp.tests/UnitTests.cs b/capnpc-csharp.tests/UnitTests.cs
index 0211867..f7d59fd 100644
--- a/capnpc-csharp.tests/UnitTests.cs
+++ b/capnpc-csharp.tests/UnitTests.cs
@@ -45,6 +45,13 @@ namespace CapnpC
             // Should not throw
         }
 
+        [TestMethod]
+        public void Test04MutualDependencies()
+        {
+            LoadAndGenerate(Resources.UnitTest4_capnp, 4);
+            // Should not throw
+        }
+
         [TestMethod]
         public void Test10ImportedNamespaces()
         {
diff --git a/capnpc-csharp/Model/SchemaModel.cs b/capnpc-csharp/Model/SchemaModel.cs
index 8d0a9fd..bd758c6 100644
--- a/capnpc-csharp/Model/SchemaModel.cs
+++ b/capnpc-csharp/Model/SchemaModel.cs
@@ -688,7 +688,7 @@ namespace CapnpC.Model
         {
             var def = ProcessNode(id, state, true, tag);
             var typeDef = def as TypeDefinition;
-            if (def == null)
+            if (typeDef == null)
                 throw new ArgumentException(
                     $"Expected node {id.StrId()} to be a TypeDefinition but got {def.GetType().Name} instead.",
                     nameof(id));
@@ -748,10 +748,10 @@ namespace CapnpC.Model
             => node.DisplayName.Substring((int)node.DisplayNamePrefixLength);
 
         public static string StrId(this Schema.Node.Reader node)
-            => $"0x{node.Id.ToString("X")}";
+            => $"0x{node.Id:X}";
 
         public static string StrId(this ulong nodeId)
-            => $"0x{nodeId.ToString("X")}";
+            => $"0x{nodeId:X}";
 
         public static NodeKind GetKind(this Schema.Node.Reader node)
         {