diff --git a/csharp/src/Google.Protobuf.Test/ExtensionSetTest.cs b/csharp/src/Google.Protobuf.Test/ExtensionSetTest.cs
index 9e60dfd19f4a..33dc50430d07 100644
--- a/csharp/src/Google.Protobuf.Test/ExtensionSetTest.cs
+++ b/csharp/src/Google.Protobuf.Test/ExtensionSetTest.cs
@@ -98,18 +98,5 @@ public void TestClone()
             Assert.AreEqual(message, other);
             Assert.AreEqual(message.CalculateSize(), message.CalculateSize());
         }
-
-        [Test]
-        public void TestImportedMultipleTImes()
-        {
-            var descriptor = UnittestWithExtension1Proto3Reflection.Descriptor.FindTypeByName<Google.Protobuf.Reflection.MessageDescriptor>("TestMessageWithExtension1");
-
-            Assert.IsNotNull(descriptor);
-            var extensionData = descriptor.GetOption(UnittestImportExtensionProto3Extensions.UnittestExtension);
-            Assert.IsNotNull(extensionData);
-
-            Assert.AreEqual(extensionData, "TestMessageWithExtension1");
-            Assert.AreEqual(descriptor.Name, "TestMessageWithExtension1");
-        }
     }
 }
diff --git a/csharp/src/Google.Protobuf/Reflection/FileDescriptor.cs b/csharp/src/Google.Protobuf/Reflection/FileDescriptor.cs
index f08fce2e07fd..b94718ff496e 100644
--- a/csharp/src/Google.Protobuf/Reflection/FileDescriptor.cs
+++ b/csharp/src/Google.Protobuf/Reflection/FileDescriptor.cs
@@ -448,7 +448,7 @@ private void CrossLink()
 
         private static IEnumerable<Extension> GetAllExtensions(FileDescriptor[] dependencies, GeneratedClrTypeInfo generatedInfo)
         {
-            return dependencies.SelectMany(GetAllDependedExtensions).Distinct(ExtensionRegistry.ExtensionComparer.Instance).Concat(GetAllGeneratedExtensions(generatedInfo));
+            return BuildDependedFileDescriptors(dependencies).SelectMany(GetAllDependedExtensions).Distinct(ExtensionRegistry.ExtensionComparer.Instance).Concat(GetAllGeneratedExtensions(generatedInfo));
         }
 
         private static IEnumerable<FileDescriptor> BuildDependedFileDescriptors(IEnumerable<FileDescriptor> dependencies)