diff --git a/Number_types/include/CGAL/GMP/Gmpfr_type.h b/Number_types/include/CGAL/GMP/Gmpfr_type.h
index b7efd1227ca..4c3002990c5 100644
--- a/Number_types/include/CGAL/GMP/Gmpfr_type.h
+++ b/Number_types/include/CGAL/GMP/Gmpfr_type.h
@@ -1170,7 +1170,7 @@ std::ostream& operator<<(std::ostream& os,const Gmpfr &a){
                 mpfr_free_str(str);
                 int i = 0;
                 size_t n = s.length();
-                sizt_t k = 0;
+                size_t k = 0;
                 while (k < n && s[n-k-1] == '0') k++; // count trailing zeros
                 if (k == n) return os << "0";
                 else if (k) {