diff --git a/include/rexy/string_base.tpp b/include/rexy/string_base.tpp
index d9c54d6..231c870 100644
--- a/include/rexy/string_base.tpp
+++ b/include/rexy/string_base.tpp
@@ -696,12 +696,13 @@ namespace rexy{
 	REXY_CPP20_CONSTEXPR auto basic_string<Char,Alloc>::_insert_impl(size_type pos, InputIt start, size_type insert_count)noexcept(is_nothrow_allocator_v<Alloc>) -> basic_string&{
 		const size_type len = this->length();
 		const size_type cap = this->capacity();
-		const size_type after_pos_count = len > pos ? len - pos : 0;
+		//add one for null terminator
+		const size_type after_pos_count = (len > pos ? len - pos : 0) + 1;
 
 		if(insert_count + len <= cap){
 
-			auto* dest_ptr = this->data() + len + insert_count - 1;
-			const auto* src_ptr = this->data() + pos + insert_count;
+			auto* dest_ptr = this->data() + len + insert_count;
+			const auto* src_ptr = this->data() + len;
 			for(size_type i = 0;i < after_pos_count;++i){
 				*dest_ptr-- = *src_ptr--;
 			}
@@ -727,8 +728,6 @@ namespace rexy{
 			}
 
 			rexy::memcpy(ptr, this->get_pointer() + pos, sizeof(value_type) * after_pos_count);
-			ptr += after_pos_count;
-			*ptr = 0; //null terminator
 			newstr.set_length(len + insert_count);
 
 			return (*this = std::move(newstr));