diff --git a/README.md b/README.md
index 4ec3695..1f37ece 100644
--- a/README.md
+++ b/README.md
@@ -62,11 +62,11 @@ class Book < ActiveRecord::Base
 
   # prefacers for the book via a join table
   has_many :forewords
-  has_many :foreworders, through: :forewords, source: :user
+  has_many :foreworders, -> { distinct }, through: :forewords, source: :user
 
   # illustrators for the book via a join table
   has_many :illustrations
-  has_many :illustrators, through: :illustrations, source: :user
+  has_many :illustrators, -> { distinct }, through: :illustrations, source: :user
 
   # editors for the book via a join table
   has_many :edits
@@ -121,16 +121,16 @@ book.contributors.where(id: editor.id)
 # => [#<User id=2, name="John W. Campbell">]
 
 book.contributors.to_sql
-# => SELECT * FROM users WHERE id IN (
+# => SELECT DISTINCT * FROM users WHERE id IN (
 #      SELECT id FROM users WHERE id = 1
 #      UNION
 #      SELECT users.id FROM users INNER JOIN prefaces ON users.id = prefaces.user_id WHERE prefaces.book_id = 1
 #      UNION
 #      SELECT users.id FROM users INNER JOIN forewords ON users.id = forewords.user_id WHERE forewords.book_id = 1
 #      UNION
-#      SELECT users.id FROM users INNER JOIN illustrations ON users.id = illustrations.user_id WHERE illustrations.book_id = 1
+#      SELECT DISTINCT users.id FROM users INNER JOIN illustrations ON users.id = illustrations.user_id WHERE illustrations.book_id = 1
 #      UNION
-#      SELECT users.id FROM users INNER JOIN edits ON users.id = edits.user_id WHERE edits.book_id = 1
+#      SELECT DISTINCT users.id FROM users INNER JOIN edits ON users.id = edits.user_id WHERE edits.book_id = 1
 #   )
 
 # example of more advanced querying e.g. preloading the union
diff --git a/spec/union_of_spec.rb b/spec/union_of_spec.rb
index cae8045..f9e72c6 100644
--- a/spec/union_of_spec.rb
+++ b/spec/union_of_spec.rb
@@ -1391,10 +1391,10 @@ def owned = where(owner: proxy_association.owner)
       has_many :foreworders, through: :forewords, source: :user
 
       has_many :illustrations
-      has_many :illustrators, through: :illustrations, source: :user
+      has_many :illustrators, -> { distinct }, through: :illustrations, source: :user
 
       has_many :edits
-      has_many :editors, through: :edits, source: :user
+      has_many :editors, -> { distinct }, through: :edits, source: :user
 
       has_many :contributors, -> { distinct }, class_name: 'User', union_of: %i[
         author
@@ -1485,7 +1485,7 @@ def owned = where(owner: proxy_association.owner)
                 )
                 UNION
                 (
-                  SELECT
+                  SELECT DISTINCT
                     users.id
                   FROM
                     users INNER JOIN illustrations ON users.id = illustrations.user_id
@@ -1494,7 +1494,7 @@ def owned = where(owner: proxy_association.owner)
                 )
                 UNION
                 (
-                  SELECT
+                  SELECT DISTINCT
                     users.id
                   FROM
                     users INNER JOIN edits ON users.id = edits.user_id