diff --git a/exprtk.hpp b/exprtk.hpp
index 7dd90e0..e0eb192 100644
--- a/exprtk.hpp
+++ b/exprtk.hpp
@@ -820,6 +820,11 @@ namespace exprtk
                return std::not_equal_to<T>()(v,v);
             }
 
+            template <typename T>
+            inline bool is_nan_impl(const T v, int_type_tag) {
+               return std::not_equal_to<T>()(v, v);
+            }
+
             template <typename T>
             inline int to_int32_impl(const T v, real_type_tag)
             {
@@ -838,6 +843,11 @@ namespace exprtk
                return static_cast<long long int>(v);
             }
 
+            template <typename T>
+            inline long long int to_int64_impl(const T v, int_type_tag) {
+               return static_cast<long long int>(v);
+            }
+
             template <typename T>
             inline bool is_true_impl(const T v)
             {
@@ -1980,6 +1990,12 @@ namespace exprtk
          return true;
       }
 
+     template <typename Iterator, typename T>
+      inline bool string_to_real(Iterator& itr_external, const Iterator end, T& t, numeric::details::int_type_tag) {
+         numeric::details::real_type_tag rtt;
+         return string_to_real(itr_external, end, t, rtt);
+      }
+
       template <typename T>
       inline bool string_to_real(const std::string& s, T& t)
       {
@@ -8564,9 +8580,9 @@ namespace exprtk
                {
                   std::size_t size = std::min((s0_r1 - s0_r0),(s1_r1 - s1_r0)) + 1;
 
-                  std::copy(str1_base_ptr_->base() + s1_r0,
-                            str1_base_ptr_->base() + s1_r0 + size,
-                            const_cast<char_ptr>(base() + s0_r0));
+                  std::copy_n(str1_base_ptr_->base() + s1_r0,
+                              size,
+                              std::back_inserter(str0_node_ptr_->ref()));
                }
             }