diff --git a/activerecord/lib/active_record/relation/predicate_builder.rb b/activerecord/lib/active_record/relation/predicate_builder.rb
index d2bb967600f57..fdb6c75405b4c 100644
--- a/activerecord/lib/active_record/relation/predicate_builder.rb
+++ b/activerecord/lib/active_record/relation/predicate_builder.rb
@@ -84,10 +84,17 @@ def expand_from_hash(attributes)
             end
 
             klass ||= AssociationQueryValue
-            queries = klass.new(associated_table, value).queries.map do |query|
-              expand_from_hash(query).reduce(&:and)
+            queries = klass.new(associated_table, value).queries.map! do |query|
+              expand_from_hash(query)
+            end
+
+            if queries.one?
+              queries.first
+            else
+              queries.map! { |query| query.reduce(&:and) }
+              queries = queries.reduce { |result, query| Arel::Nodes::Or.new(result, query) }
+              Arel::Nodes::Grouping.new(queries)
             end
-            queries.reduce(&:or)
           elsif table.aggregated_with?(key)
             mapping = table.reflect_on_aggregation(key).mapping
             values = value.nil? ? [nil] : Array.wrap(value)
diff --git a/activerecord/test/cases/associations/inner_join_association_test.rb b/activerecord/test/cases/associations/inner_join_association_test.rb
index 1ec349aa73487..eb677413904d3 100644
--- a/activerecord/test/cases/associations/inner_join_association_test.rb
+++ b/activerecord/test/cases/associations/inner_join_association_test.rb
@@ -110,7 +110,7 @@ def test_join_association_conditions_support_string_and_arel_expressions
 
   def test_join_conditions_allow_nil_associations
     authors = Author.includes(:essays).where(essays: { id: nil })
-    assert_equal 2, authors.count
+    assert_equal 1, authors.count
   end
 
   def test_find_with_implicit_inner_joins_without_select_does_not_imply_readonly
diff --git a/activerecord/test/cases/relation/where_chain_test.rb b/activerecord/test/cases/relation/where_chain_test.rb
index 991efa649ca05..d5debc1d0488b 100644
--- a/activerecord/test/cases/relation/where_chain_test.rb
+++ b/activerecord/test/cases/relation/where_chain_test.rb
@@ -3,18 +3,14 @@
 require "cases/helper"
 require "models/post"
 require "models/author"
+require "models/essay"
 require "models/comment"
 require "models/categorization"
 
 
 module ActiveRecord
   class WhereChainTest < ActiveRecord::TestCase
-    fixtures :posts, :authors
-
-    def setup
-      super
-      @name = "title"
-    end
+    fixtures :posts, :authors, :essays
 
     def test_missing_with_association
       assert posts(:authorless).author.blank?
@@ -40,7 +36,7 @@ def test_not_with_nil
     end
 
     def test_association_not_eq
-      expected = Comment.arel_table[@name].not_eq(Arel::Nodes::BindParam.new(1))
+      expected = Comment.arel_table["title"].not_eq(Arel::Nodes::BindParam.new(1))
       relation = Post.joins(:comments).where.not(comments: { title: "hello" })
       assert_equal(expected.to_sql, relation.where_clause.ast.to_sql)
     end
@@ -93,6 +89,13 @@ def test_rewhere_with_one_overwriting_condition_and_one_unrelated
       assert_equal expected.where_clause, relation.where_clause
     end
 
+    def test_rewhere_with_polymorphic_association
+      relation = Essay.where(writer: authors(:david)).rewhere(writer_id: "Mary")
+      expected = Essay.where(writer: authors(:mary))
+
+      assert_equal expected, relation
+    end
+
     def test_rewhere_with_range
       relation = Post.where(comments_count: 1..3).rewhere(comments_count: 3..5)
 
diff --git a/activerecord/test/fixtures/essays.yml b/activerecord/test/fixtures/essays.yml
index 9d15d82359d62..542e37f811c2c 100644
--- a/activerecord/test/fixtures/essays.yml
+++ b/activerecord/test/fixtures/essays.yml
@@ -4,3 +4,8 @@ david_modest_proposal:
   writer_id: David
   category_id: General
   author_id: David
+
+mary_stay_home:
+  name: Stay Home
+  writer_type: Author
+  writer_id: Mary