diff --git a/activerecord/lib/active_record/relation/query_methods.rb b/activerecord/lib/active_record/relation/query_methods.rb
index c80f573f01..110cfc6d0b 100644
--- a/activerecord/lib/active_record/relation/query_methods.rb
+++ b/activerecord/lib/active_record/relation/query_methods.rb
@@ -1513,8 +1513,11 @@ module ActiveRecord
         values = other.values
         STRUCTURAL_OR_METHODS.reject do |method|
           v1, v2 = @values[method], values[method]
-          v1 = v1.uniq if v1.is_a?(Array)
-          v2 = v2.uniq if v2.is_a?(Array)
+          if v1.is_a?(Array)
+            next true unless v2.is_a?(Array)
+            v1 = v1.uniq
+            v2 = v2.uniq
+          end
           v1 == v2 || (!v1 || v1.empty?) && (!v2 || v2.empty?)
         end
       end
diff --git a/activerecord/test/cases/relation/merging_test.rb b/activerecord/test/cases/relation/merging_test.rb
index d7f6b43cec..0da5dd7cbc 100644
--- a/activerecord/test/cases/relation/merging_test.rb
+++ b/activerecord/test/cases/relation/merging_test.rb
@@ -43,7 +43,7 @@ class RelationMergingTest < ActiveRecord::TestCase
     assert_equal [mary], david_and_mary.and(mary_and_bob)
     assert_equal authors, david_and_mary.or(mary_and_bob)
 
-    david_and_bob = Author.where(id: david).or(Author.where(name: "Bob")).order(:id)
+    david_and_bob = Author.where(id: david).or(Author.where(name: "Bob"))
 
     assert_equal [david], david_and_mary.merge(david_and_bob)
     assert_equal [david], david_and_mary.merge(david_and_bob, rewhere: true)
@@ -96,7 +96,7 @@ class RelationMergingTest < ActiveRecord::TestCase
     assert_equal [mary], david_and_mary.and(mary_and_bob)
     assert_equal authors, david_and_mary.or(mary_and_bob)
 
-    david_and_bob = Author.where(id: david).or(Author.where(name: "Bob")).order(:id)
+    david_and_bob = Author.where(id: david).or(Author.where(name: "Bob"))
 
     assert_equal [david], david_and_mary.merge(david_and_bob)
     assert_equal [david], david_and_mary.merge(david_and_bob, rewhere: true)
@@ -149,7 +149,7 @@ class RelationMergingTest < ActiveRecord::TestCase
     assert_equal [mary], david_and_mary.and(mary_and_bob)
     assert_equal authors, david_and_mary.or(mary_and_bob)
 
-    david_and_bob = Author.where(id: david).or(Author.where(name: "Bob")).order(:id)
+    david_and_bob = Author.where(id: david).or(Author.where(name: "Bob"))
 
     assert_equal [david], david_and_mary.merge(david_and_bob)
     assert_equal [david], david_and_mary.merge(david_and_bob, rewhere: true)
diff --git a/activerecord/test/cases/relation/or_test.rb b/activerecord/test/cases/relation/or_test.rb
index 4e6a78e283..b3dbbc4d6d 100644
--- a/activerecord/test/cases/relation/or_test.rb
+++ b/activerecord/test/cases/relation/or_test.rb
@@ -84,11 +84,12 @@ module ActiveRecord
     def test_or_with_unscope_order
       expected = Post.where("id = 1 or id = 2")
       assert_equal expected, Post.order("body asc").where("id = 1").unscope(:order).or(Post.where("id = 2")).to_a
+      assert_equal expected, Post.order(:id).where("id = 1").or(Post.order(:id).where("id = 2").unscope(:order)).to_a
     end
 
     def test_or_with_incompatible_unscope
       error = assert_raises ArgumentError do
-        Post.order("body asc").where("id = 1").or(Post.order("body asc").where("id = 2").unscope(:order)).to_a
+        Post.order("body asc").where("id = 1").unscope(:order).or(Post.order("body asc").where("id = 2")).to_a
       end
 
       assert_equal "Relation passed to #or must be structurally compatible. Incompatible values: [:order]", error.message