Mocking a type with an internal constructor using Moq

I'm trying to mock a class from the Microsoft Sync Framework. It only has an internal constructor. When I try the following:

var fullEnumerationContextMock = new Mock<FullEnumerationContext>();

I get this error:

System.NotSupportedException: Parent does not have a default constructor. The default constructor must be explicitly defined.

This is the stack trace:

System.Reflection.Emit.TypeBuilder.DefineDefaultConstructorNoLock(MethodAttributes attributes) System.Reflection.Emit.TypeBuilder.DefineDefaultConstructor(MethodAttributes attributes) System.Reflection.Emit.TypeBuilder.CreateTypeNoLock() System.Reflection.Emit.TypeBuilder.CreateType() Castle.DynamicProxy.Generators.Emitters.AbstractTypeEmitter.BuildType() Castle.DynamicProxy.Generators.ClassProxyGenerator.GenerateCode(Type[] interfaces, ProxyGenerationOptions options) Castle.DynamicProxy.DefaultProxyBuilder.CreateClassProxy(Type classToProxy, Type[] additionalInterfacesToProxy, ProxyGenerationOptions options) Castle.DynamicProxy.ProxyGenerator.CreateClassProxyType(Type classToProxy, Type[] additionalInterfacesToProxy, ProxyGenerationOptions options) Castle.DynamicProxy.ProxyGenerator.CreateClassProxy(Type classToProxy, Type[] additionalInterfacesToProxy, ProxyGenerationOptions options, Object[] constructorArguments, IInterceptor[] interceptors) Castle.DynamicProxy.ProxyGenerator.CreateClassProxy(Type classToProxy, Type[] additionalInterfacesToProxy, ProxyGenerationOptions options, IInterceptor[] interceptors) Castle.DynamicProxy.ProxyGenerator.CreateClassProxy(Type classToProxy, Type[] additionalInterfacesToProxy, IInterceptor[] interceptors) Moq.Mock1.<InitializeInstance>b__0() Moq.PexProtector.Invoke(Action action) Moq.Mock1.InitializeInstance()

How can I work round this?