diff --git a/src/utf8/checked.h b/src/utf8/checked.h
index 0e662e2..83015f9 100644
--- a/src/utf8/checked.h
+++ b/src/utf8/checked.h
@@ -31,6 +31,7 @@ DEALINGS IN THE SOFTWARE.
 #include "core.h"
 #include <stdexcept>
 #include <cassert>
+#include <cstddef>
 
 namespace utf8
 {
@@ -310,7 +311,7 @@ namespace utf8
 		typename octet_iterator,
 		typename error_policy=ErrorPolicyThrow<octet_iterator>
 	>
-    class iterator : public std::iterator <std::bidirectional_iterator_tag, uint32_t> {
+    class iterator : public std::iterator <std::bidirectional_iterator_tag, uint32_t, std::ptrdiff_t, uint32_t*, uint32_t> {
       octet_iterator it;
       octet_iterator range_start;
       octet_iterator range_end;