diff --git a/lib/bunny/channel.rb b/lib/bunny/channel.rb
index 607262b6..b1d4d444 100644
--- a/lib/bunny/channel.rb
+++ b/lib/bunny/channel.rb
@@ -1789,7 +1789,7 @@ def handle_basic_return(basic_return, properties, content)
     # @private
     def handle_ack_or_nack(delivery_tag_before_offset, multiple, nack)
       delivery_tag          = delivery_tag_before_offset + @delivery_tag_offset
-      confirmed_range_start = multiple ? @delivery_tag_offset + 1 : delivery_tag
+      confirmed_range_start = multiple ? @delivery_tag_offset + @unconfirmed_set.min : delivery_tag
       confirmed_range_end   = delivery_tag
       confirmed_range       = (confirmed_range_start..confirmed_range_end)