diff --git a/libs/group/include/psemek/group/cyclic.hpp b/libs/group/include/psemek/group/cyclic.hpp
index 601d3340..29b2bce8 100644
--- a/libs/group/include/psemek/group/cyclic.hpp
+++ b/libs/group/include/psemek/group/cyclic.hpp
@@ -52,7 +52,7 @@ namespace psemek::group
 
 		struct value_iterator
 		{
-			using difference_type = int;
+			using difference_type = Repr;
 			using value_type = cyclic<N, Repr>;
 			using pointer = value_type *;
 			using reference	= value_type &;
@@ -75,6 +75,11 @@ namespace psemek::group
 			{
 				return it1.repr == it2.repr;
 			}
+
+			friend auto operator - (value_iterator const & it1, value_iterator const & it2)
+			{
+				return it2.repr - it1.repr;
+			}
 		};
 
 		static auto values()
diff --git a/libs/group/include/psemek/group/dihedral.hpp b/libs/group/include/psemek/group/dihedral.hpp
index 33899469..95e2e382 100644
--- a/libs/group/include/psemek/group/dihedral.hpp
+++ b/libs/group/include/psemek/group/dihedral.hpp
@@ -84,7 +84,7 @@ namespace psemek::group
 
 		struct value_iterator
 		{
-			using difference_type = int;
+			using difference_type = Repr;
 			using value_type = dihedral<N, Repr>;
 			using pointer = value_type *;
 			using reference	= value_type &;
@@ -107,6 +107,11 @@ namespace psemek::group
 			{
 				return it1.repr == it2.repr;
 			}
+
+			friend auto operator - (value_iterator const & it1, value_iterator const & it2)
+			{
+				return it2.repr - it1.repr;
+			}
 		};
 
 		static auto values()