diff --git a/lib/redmine/sort_criteria.rb b/lib/redmine/sort_criteria.rb
index 448c13d41..b527fe4f0 100644
--- a/lib/redmine/sort_criteria.rb
+++ b/lib/redmine/sort_criteria.rb
@@ -90,6 +90,7 @@ module Redmine
 
     def normalize!
       self.reject! {|s| s.first.blank? }
+      self.uniq! {|s| s.first }
       self.collect! {|s| s = Array(s); [s.first, (s.last == false || s.last.to_s == 'desc') ? 'desc' : 'asc']}
       self.replace self.first(3)
     end
diff --git a/test/unit/query_test.rb b/test/unit/query_test.rb
index 56ec82d14..2ea831c5d 100644
--- a/test/unit/query_test.rb
+++ b/test/unit/query_test.rb
@@ -1610,12 +1610,12 @@ class QueryTest < ActiveSupport::TestCase
   def test_sort_criteria_should_have_only_first_three_elements
     q = IssueQuery.new
     q.sort_criteria = [['priority', 'desc'], ['tracker', 'asc'], ['priority', 'asc'], ['id', 'asc'], ['project', 'asc'], ['subject', 'asc']]
-    assert_equal [['priority', 'desc'], ['tracker', 'asc'], ['priority', 'asc']], q.sort_criteria
+    assert_equal [['priority', 'desc'], ['tracker', 'asc'], ['id', 'asc']], q.sort_criteria
   end
 
-  def test_sort_criteria_should_remove_blank_keys
+  def test_sort_criteria_should_remove_blank_or_duplicate_keys
     q = IssueQuery.new
-    q.sort_criteria = [['priority', 'desc'], [nil, 'desc'], ['', 'asc'], ['project', 'asc']]
+    q.sort_criteria = [['priority', 'desc'], [nil, 'desc'], ['', 'asc'], ['priority', 'asc'], ['project', 'asc']]
     assert_equal [['priority', 'desc'], ['project', 'asc']], q.sort_criteria
   end