diff --git a/lib/net/imap/sequence_set.rb b/lib/net/imap/sequence_set.rb
index 827d331fe..28a51fc9c 100644
--- a/lib/net/imap/sequence_set.rb
+++ b/lib/net/imap/sequence_set.rb
@@ -1720,7 +1720,7 @@ def find_ordered_index(number)
       #
       # Related: #[], #slice, #ordered_at
       def at(index)
-        seek_number_in_minmaxes(minmaxes, index)
+        export_num sorted_set_num_at Integer index.to_int
       end
 
       # :call-seq: ordered_at(index) -> integer or nil
@@ -1733,7 +1733,7 @@ def at(index)
       #
       # Related: #[], #slice, #ordered_at
       def ordered_at(index)
-        seek_number_in_minmaxes(each_entry_minmax, index)
+        export_num ordered_list_num_at Integer index.to_int
       end
 
       # :call-seq:
@@ -2377,15 +2377,22 @@ def bsearch_range(num)  = (min, max = bsearch_minmax(num)) && (min..max)
       ######################################################################{{{2
       # Number indexing methods
 
+      def sorted_set_num_at(index)
+        seek_number_in_minmaxes(minmaxes, index)
+      end
+
+      def ordered_list_num_at(index)
+        seek_number_in_minmaxes(each_entry_minmax, index)
+      end
+
       def seek_number_in_minmaxes(minmaxes, index)
-        index = Integer(index.to_int)
         if index.negative?
           reverse_each_minmax_with_index(minmaxes) do |min, max, idx_min, idx_max|
-            idx_min <= index and return export_num(min + (index - idx_min))
+            idx_min <= index and return min + (index - idx_min)
           end
         else
           each_minmax_with_index(minmaxes) do |min, _, idx_min, idx_max|
-            index <= idx_max and return export_num(min + (index - idx_min))
+            index <= idx_max and return min + (index - idx_min)
           end
         end
         nil
@@ -2414,8 +2421,8 @@ def slice_length(start, length)
         start  = Integer(start.to_int)
         length = Integer(length.to_int)
         raise ArgumentError, "length must be positive" unless length.positive?
-        last = start + length - 1 unless start.negative? && start.abs <= length
-        slice_range(start..last)
+        stop   = start + length unless start.negative? && start.abs <= length
+        slice_range(start...stop)
       end
 
       def slice_range(range)
@@ -2423,7 +2430,7 @@ def slice_range(range)
         last  = range.end   || -1
         if range.exclude_end?
           return remain_frozen_empty if last.zero?
-          last -= 1 if range.end && last != STAR_INT
+          last -= 1 if range.end
         end
         if (first * last).positive? && last < first
           remain_frozen_empty