diff --git a/include/chaiscript/dispatchkit/type_conversions.hpp b/include/chaiscript/dispatchkit/type_conversions.hpp
index 8b57d79c..8ba6bfc8 100644
--- a/include/chaiscript/dispatchkit/type_conversions.hpp
+++ b/include/chaiscript/dispatchkit/type_conversions.hpp
@@ -30,6 +30,25 @@ namespace chaiscript
 {
   namespace exception
   {
+    /// \brief Error thrown when there's a problem with type conversion
+    class conversion_error
+    {
+       public:
+         conversion_error(const Type_Info& t_to, const Type_Info& t_from, const utility::Static_String what): to(t_to),
+         from(t_from), m_what(std::move(what)) {};
+
+        const char * what() const noexcept
+        {
+            return m_what.c_str();
+        }
+
+       private:
+         const Type_Info&  to;
+         const Type_Info&  from;
+         utility::Static_String m_what;
+
+    };
+
     class bad_boxed_dynamic_cast : public bad_boxed_cast
     {
       public:
@@ -362,10 +381,14 @@ namespace chaiscript
         return cache;
       }
 
+
       void add_conversion(const std::shared_ptr<detail::Type_Conversion_Base> &conversion)
       {
         chaiscript::detail::threading::unique_lock<chaiscript::detail::threading::shared_mutex> l(m_mutex);
-        /// \todo error if a conversion already exists
+        if (has_conversion(conversion)) {
+            throw exception::conversion_error(conversion->to(), conversion->from(),
+                    "Trying to re-insert an existing conversion!");
+        }
         m_conversions.insert(conversion);
         m_convertableTypes.insert({conversion->to().bare_type_info(), conversion->from().bare_type_info()});
         m_num_types = m_convertableTypes.size();
@@ -452,6 +475,12 @@ namespace chaiscript
         return find_bidir(to, from) != m_conversions.end();
       }
 
+      /// \brief has_conversion overloaded for Type_Conversion_Base parameter
+      bool has_conversion(const std::shared_ptr<detail::Type_Conversion_Base> &conversion)
+      {
+          return has_conversion(conversion->to(), conversion->from());
+      }
+
       std::shared_ptr<detail::Type_Conversion_Base> get_conversion(const Type_Info &to, const Type_Info &from) const
       {
         chaiscript::detail::threading::shared_lock<chaiscript::detail::threading::shared_mutex> l(m_mutex);