diff --git a/code/compiler/11/definition.cpp b/code/compiler/11/definition.cpp
index 79d53af..5f820b7 100644
--- a/code/compiler/11/definition.cpp
+++ b/code/compiler/11/definition.cpp
@@ -58,7 +58,7 @@ void definition_defn::generate_llvm(llvm_context& ctx) {
 
 void definition_data::insert_types(type_env_ptr& env) {
     this->env = env;
-    env->bind_type(name, type_ptr(new type_data(name)));
+    env->bind_type(name, type_ptr(new type_data(name, vars.size())));
 }
 
 void definition_data::insert_constructors() const {
diff --git a/code/compiler/11/parsed_type.cpp b/code/compiler/11/parsed_type.cpp
index 4644d52..c69e50a 100644
--- a/code/compiler/11/parsed_type.cpp
+++ b/code/compiler/11/parsed_type.cpp
@@ -9,6 +9,7 @@ type_ptr parsed_type_app::to_type(
     if(parent_type == nullptr) throw 0;
     type_base* base_type;
     if(!(base_type = dynamic_cast<type_base*>(parent_type.get()))) throw 0;
+    if(base_type->arity != arguments.size()) throw 0;
 
     type_app* new_app = new type_app(std::move(parent_type));
     type_ptr to_return(new_app);
diff --git a/code/compiler/11/type.hpp b/code/compiler/11/type.hpp
index 6c524aa..4583f45 100644
--- a/code/compiler/11/type.hpp
+++ b/code/compiler/11/type.hpp
@@ -53,8 +53,8 @@ struct type_data : public type_base {
 
     std::map<std::string, constructor> constructors;
 
-    type_data(std::string n)
-        : type_base(std::move(n)) {}
+    type_data(std::string n, int32_t a = 0)
+        : type_base(std::move(n), a) {}
 };
 
 struct type_arr : public type {