diff --git a/app/models/issue.rb b/app/models/issue.rb
index 5a49b0d..8777a11 100644
--- a/app/models/issue.rb
+++ b/app/models/issue.rb
@@ -819,12 +819,12 @@ class Issue < ActiveRecord::Base
     end
   end
 
-  # Returns the previous assignee if changed
+  # Returns the previous assignee (user or group) if changed
   def assigned_to_was
     # assigned_to_id_was is reset before after_save callbacks
     user_id = @previous_assigned_to_id || assigned_to_id_was
     if user_id && user_id != assigned_to_id
-      @assigned_to_was ||= User.find_by_id(user_id)
+      @assigned_to_was ||= Principal.find_by_id(user_id)
     end
   end
 
diff --git a/test/unit/issue_test.rb b/test/unit/issue_test.rb
index 33635e7..72157e5 100644
--- a/test/unit/issue_test.rb
+++ b/test/unit/issue_test.rb
@@ -2591,4 +2591,12 @@ class IssueTest < ActiveSupport::TestCase
     issue.tracker = Tracker.find(2)
     assert_equal IssueStatus.find(3), issue.status
   end
+
+  def test_assigned_to_was_with_a_group
+    group = Group.find(10)
+
+    issue = Issue.generate!(:assigned_to => group)
+    issue.reload.assigned_to = nil
+    assert_equal group, issue.assigned_to_was
+  end
 end