diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index f6cd5efb4537ddcf3a7b897f0b97c95df9dddf3f..755fb32c3ffa6c0451bd51eb14bc92dd7d241dd8 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,9 @@
+*   Fix how to calculate associated class name when using `habtm` namespaced.
+
+    Fixes #14709.
+
+    *Kassio Borges*
+
 *   `change_column_default` allows `[]` as argument to `change_column_default`.
 
     Fixes #11586.
diff --git a/activerecord/lib/active_record/associations/builder/has_and_belongs_to_many.rb b/activerecord/lib/active_record/associations/builder/has_and_belongs_to_many.rb
index e47227737485b4f73792d4a7db0b44f1739230fa..ad781e50c9a5916c178642dd0bc641b576437dc8 100644
--- a/activerecord/lib/active_record/associations/builder/has_and_belongs_to_many.rb
+++ b/activerecord/lib/active_record/associations/builder/has_and_belongs_to_many.rb
@@ -23,7 +23,11 @@ def self.build(lhs_class, name, options)
           KnownTable.new options[:join_table].to_s
         else
           class_name = options.fetch(:class_name) {
-            name.to_s.camelize.singularize
+            model_name = name.to_s.camelize.singularize
+            if parent_name = lhs_class.parent_name.presence
+              model_name = model_name.prepend("#{parent_name}::")
+            end
+            model_name
           }
           KnownClass.new lhs_class, class_name
         end
diff --git a/activerecord/test/cases/associations/has_and_belongs_to_many_associations_test.rb b/activerecord/test/cases/associations/has_and_belongs_to_many_associations_test.rb
index cfdfff6af9d2a741c65e7e8ab15bd77ffecb9a3f..878f1877dbddfd37b362c40672541cb13caaa744 100644
--- a/activerecord/test/cases/associations/has_and_belongs_to_many_associations_test.rb
+++ b/activerecord/test/cases/associations/has_and_belongs_to_many_associations_test.rb
@@ -22,6 +22,9 @@
 require 'models/country'
 require 'models/treaty'
 require 'models/vertex'
+require 'models/publisher'
+require 'models/publisher/article'
+require 'models/publisher/magazine'
 require 'active_support/core_ext/string/conversions'
 
 class ProjectWithAfterCreateHook < ActiveRecord::Base
@@ -848,4 +851,13 @@ def test_association_with_validate_false_does_not_run_associated_validation_call
   def test_custom_join_table
     assert_equal 'edges', Vertex.reflect_on_association(:sources).join_table
   end
+
+  def test_namespaced_habtm
+    magazine = Publisher::Magazine.create
+    article = Publisher::Article.create
+    magazine.articles << article
+    magazine.save
+
+    assert_includes magazine.articles, article
+  end
 end
diff --git a/activerecord/test/models/publisher.rb b/activerecord/test/models/publisher.rb
new file mode 100644
index 0000000000000000000000000000000000000000..0d4a7f92351a03de7cc8e9ff1fa44d1424627bc9
--- /dev/null
+++ b/activerecord/test/models/publisher.rb
@@ -0,0 +1,2 @@
+module Publisher
+end
diff --git a/activerecord/test/models/publisher/article.rb b/activerecord/test/models/publisher/article.rb
new file mode 100644
index 0000000000000000000000000000000000000000..03a277bbddfd71b8fa716ff596e323d2f2f08ef2
--- /dev/null
+++ b/activerecord/test/models/publisher/article.rb
@@ -0,0 +1,3 @@
+class Publisher::Article < ActiveRecord::Base
+  has_and_belongs_to_many :magazines
+end
diff --git a/activerecord/test/models/publisher/magazine.rb b/activerecord/test/models/publisher/magazine.rb
new file mode 100644
index 0000000000000000000000000000000000000000..82e1a14008ec447f6ef9786262b409a0f7f130d0
--- /dev/null
+++ b/activerecord/test/models/publisher/magazine.rb
@@ -0,0 +1,3 @@
+class Publisher::Magazine < ActiveRecord::Base
+  has_and_belongs_to_many :articles
+end
diff --git a/activerecord/test/schema/schema.rb b/activerecord/test/schema/schema.rb
index da3074e90f2f34c3acfa3eae8070466ee24e21dd..a78074d53042df2af3289293b16eda0be69171b9 100644
--- a/activerecord/test/schema/schema.rb
+++ b/activerecord/test/schema/schema.rb
@@ -62,6 +62,14 @@ def create_table(*args, &block)
     t.string :name
   end
 
+  create_table :articles, force: true do |t|
+  end
+
+  create_table :articles_magazines, force: true do |t|
+    t.references :article
+    t.references :magazine
+  end
+
   create_table :audit_logs, force: true do |t|
     t.column :message, :string, null: false
     t.column :developer_id, :integer, null: false
@@ -385,6 +393,9 @@ def create_table(*args, &block)
     t.column :custom_lock_version, :integer
   end
 
+  create_table :magazines, force: true do |t|
+  end
+
   create_table :mateys, id: false, force: true do |t|
     t.column :pirate_id, :integer
     t.column :target_id, :integer