diff --git a/include/boost/uuid/detail/throw_invalid_uuid.hpp b/include/boost/uuid/detail/throw_invalid_uuid.hpp
index b546c55..9b15142 100644
--- a/include/boost/uuid/detail/throw_invalid_uuid.hpp
+++ b/include/boost/uuid/detail/throw_invalid_uuid.hpp
@@ -10,6 +10,7 @@
 #include <boost/config.hpp>
 #include <stdexcept>
 #include <cstdio>
+#include <cstddef>
 
 namespace boost {
 namespace uuids {
@@ -29,10 +30,10 @@ BOOST_CXX14_CONSTEXPR inline char const* fc_error_to_string( from_chars_error er
     }
 }
 
-BOOST_NORETURN inline void throw_invalid_uuid( int pos, from_chars_error err )
+BOOST_NORETURN inline void throw_invalid_uuid( std::ptrdiff_t pos, from_chars_error err )
 {
     char buffer[ 128 ];
-    std::snprintf( buffer, sizeof( buffer ), "Invalid UUID string at position %d: %s", pos, fc_error_to_string( err ) );
+    std::snprintf( buffer, sizeof( buffer ), "Invalid UUID string at position %td: %s", pos, fc_error_to_string( err ) );
 
     BOOST_THROW_EXCEPTION( std::runtime_error( buffer ) );
 }
diff --git a/include/boost/uuid/detail/uuid_from_string.hpp b/include/boost/uuid/detail/uuid_from_string.hpp
index fdeaf13..b3724c5 100644
--- a/include/boost/uuid/detail/uuid_from_string.hpp
+++ b/include/boost/uuid/detail/uuid_from_string.hpp
@@ -10,7 +10,6 @@
 #include <boost/uuid/detail/throw_invalid_uuid.hpp>
 #include <boost/uuid/detail/cstring.hpp>
 #include <boost/config.hpp>
-#include <string>
 
 namespace boost {
 namespace uuids {
@@ -27,12 +26,12 @@ uuid uuid_from_string( Ch const* first, Ch const* last )
 
     if( r.ec != from_chars_error::none )
     {
-        detail::throw_invalid_uuid( static_cast<int>( r.ptr - first ), r.ec );
+        detail::throw_invalid_uuid( r.ptr - first, r.ec );
     }
 
     if( r.ptr != last )
     {
-        detail::throw_invalid_uuid( static_cast<int>( r.ptr - first ), from_chars_error::unexpected_extra_input );
+        detail::throw_invalid_uuid( r.ptr - first, from_chars_error::unexpected_extra_input );
     }
 
     return u;
diff --git a/include/boost/uuid/string_generator.hpp b/include/boost/uuid/string_generator.hpp
index 83b3cb5..314286e 100644
--- a/include/boost/uuid/string_generator.hpp
+++ b/include/boost/uuid/string_generator.hpp
@@ -33,7 +33,7 @@ public:
     using result_type = uuid;
 
     template<class CharIterator>
-    BOOST_CXX14_CONSTEXPR uuid operator()( CharIterator first, CharIterator last, int& pos, from_chars_error& err ) const noexcept
+    BOOST_CXX14_CONSTEXPR uuid operator()( CharIterator first, CharIterator last, std::ptrdiff_t& pos, from_chars_error& err ) const noexcept
     {
         uuid u;
 
@@ -170,7 +170,7 @@ public:
     template<class CharIterator>
     BOOST_CXX14_CONSTEXPR uuid operator()( CharIterator first, CharIterator last ) const
     {
-        int pos = 0;
+        std::ptrdiff_t pos = 0;
         from_chars_error err = {};
 
         uuid r = operator()( first, last, pos, err );