diff --git a/app/finders/issuable_finder.rb b/app/finders/issuable_finder.rb
index 15b5d6ab34..3d5e8b6fbe 100644
--- a/app/finders/issuable_finder.rb
+++ b/app/finders/issuable_finder.rb
@@ -190,8 +190,10 @@ class IssuableFinder
 
   def by_project(items)
     items =
-      if projects
-        items.of_projects(projects).references(:project)
+      if project?
+        items.of_projects(projects).references_project
+      elsif projects
+        items.merge(projects.reorder(nil)).join_project
       else
         items.none
       end
@@ -206,7 +208,9 @@ class IssuableFinder
   end
 
   def sort(items)
-    items.sort(params[:sort])
+    # Ensure we always have an explicit sort order (instead of inheriting
+    # multiple orders when combining ActiveRecord::Relation objects).
+    params[:sort] ? items.sort(params[:sort]) : items.reorder(id: :desc)
   end
 
   def by_assignee(items)
diff --git a/app/models/concerns/issuable.rb b/app/models/concerns/issuable.rb
index 492a026add..97d3cb18f4 100644
--- a/app/models/concerns/issuable.rb
+++ b/app/models/concerns/issuable.rb
@@ -35,6 +35,9 @@ module Issuable
     scope :order_milestone_due_desc, -> { joins(:milestone).reorder('milestones.due_date DESC, milestones.id DESC') }
     scope :order_milestone_due_asc, -> { joins(:milestone).reorder('milestones.due_date ASC, milestones.id ASC') }
 
+    scope :join_project, -> { joins(:project) }
+    scope :references_project, -> { references(:project) }
+
     delegate :name,
              :email,
              to: :author,
diff --git a/app/models/merge_request.rb b/app/models/merge_request.rb
index 2eb03b8ba5..1e8d9908f0 100644
--- a/app/models/merge_request.rb
+++ b/app/models/merge_request.rb
@@ -134,6 +134,9 @@ class MergeRequest < ActiveRecord::Base
   scope :closed, -> { with_state(:closed) }
   scope :closed_and_merged, -> { with_states(:closed, :merged) }
 
+  scope :join_project, -> { joins(:target_project) }
+  scope :references_project, -> { references(:target_project) }
+
   def self.reference_prefix
     '!'
   end