diff --git a/include/nbind/BindClass.h b/include/nbind/BindClass.h
index 8c8bd81..705adb7 100644
--- a/include/nbind/BindClass.h
+++ b/include/nbind/BindClass.h
@@ -237,8 +237,14 @@ BindClassBase &BindWrapper<Bound> :: getBindClass() {
 
 template <class Bound>
 void BindWrapper<Bound> :: testInstance(v8::Local<v8::Object> arg) {
+	BindClassBase &bindClass = getBindClass();
+
+	if(bindClass.superTemplate.IsEmpty()) {
+		throw(std::runtime_error("Unbound type"));
+	}
+
 	if(
-		!Nan::New(getBindClass().superTemplate)->HasInstance(arg) ||
+		!Nan::New(bindClass.superTemplate)->HasInstance(arg) ||
 		arg->InternalFieldCount() != 1
 	) {
 		throw(std::runtime_error("Type mismatch"));
diff --git a/include/nbind/v8/ValueObj.h b/include/nbind/v8/ValueObj.h
index 8b84b16..eccf8da 100644
--- a/include/nbind/v8/ValueObj.h
+++ b/include/nbind/v8/ValueObj.h
@@ -49,7 +49,14 @@ static inline WireType makeExternal(TypeFlags flags, TargetType *ptr, ArgType &&
 #endif // DUPLICATE_POINTERS
 
 	unsigned int constructorNum = BindClass<BaseType>::getInstance().wrapperConstructorNum;
-	v8::Local<v8::Function> constructor = Overloader::getDef(constructorNum).constructorJS->GetFunction();
+	Nan::Callback *constructorJS = Overloader::getDef(constructorNum).constructorJS;
+
+	if(constructorJS == nullptr) {
+		Nan::ThrowError("Unbound type");
+		return(Nan::Undefined());
+	}
+
+	v8::Local<v8::Function> constructor = constructorJS->GetFunction();
 
 	// TODO: first argument should be a unique marker of some kind.