diff --git a/app/models/project.rb b/app/models/project.rb
index ace0132e..165cf513 100644
--- a/app/models/project.rb
+++ b/app/models/project.rb
@@ -5,6 +5,8 @@
 class Project < ApplicationRecord
   before_validation :check_unique_not_null, on: :create
   validates :identifier, presence: true, uniqueness: { scope: :locale }
+  validate :identifier_cannot_be_taken_by_another_user
+  validates :locale, presence: true, unless: :user_id
   belongs_to :parent, class_name: 'Project', foreign_key: 'remixed_from_id', optional: true, inverse_of: :remixes
   has_many :components, -> { order(default: :desc, name: :asc) }, dependent: :destroy, inverse_of: :project
   has_many :remixes, class_name: 'Project', foreign_key: 'remixed_from_id', dependent: :nullify, inverse_of: :parent
@@ -15,6 +17,11 @@ class Project < ApplicationRecord
 
   def check_unique_not_null
     self.identifier ||= PhraseIdentifier.generate
-    self.identifier = PhraseIdentifier.generate until Project.find_by(identifier: self.identifier, locale:).nil?
+  end
+
+  def identifier_cannot_be_taken_by_another_user
+    return if Project.where(identifier: self.identifier).where.not(user_id:).empty?
+
+    errors.add(:identifier, "can't be taken by another user")
   end
 end
diff --git a/lib/concepts/project/operations/create_remix.rb b/lib/concepts/project/operations/create_remix.rb
index 38a9cdf2..78a103dd 100644
--- a/lib/concepts/project/operations/create_remix.rb
+++ b/lib/concepts/project/operations/create_remix.rb
@@ -32,10 +32,7 @@ def remix_project(response, params, user_id, original_project)
       end
 
       def create_remix(original_project, params, user_id)
-        remix = original_project.dup.tap do |proj|
-          proj.user_id = user_id
-          proj.remixed_from_id = original_project.id
-        end
+        remix = format_project(original_project, user_id)
 
         original_project.images.each do |image|
           remix.images.attach(image.blob)
@@ -47,6 +44,15 @@ def create_remix(original_project, params, user_id)
 
         remix
       end
+
+      def format_project(original_project, user_id)
+        original_project.dup.tap do |proj|
+          proj.user_id = user_id
+          proj.remixed_from_id = original_project.id
+          proj.identifier = PhraseIdentifier.generate
+          proj.locale = nil
+        end
+      end
     end
   end
 end
diff --git a/lib/phrase_identifier.rb b/lib/phrase_identifier.rb
index f0aeb96d..5c90f5a8 100644
--- a/lib/phrase_identifier.rb
+++ b/lib/phrase_identifier.rb
@@ -2,6 +2,11 @@
 
 class PhraseIdentifier
   def self.generate
-    Word.order(Arel.sql('RANDOM()')).take(3).pluck(:word).join('-')
+    phrase = Word.order(Arel.sql('RANDOM()')).take(3).pluck(:word).join('-') until unique?(phrase)
+    phrase
+  end
+
+  def self.unique?(phrase)
+    !phrase.nil? && Project.find_by(identifier: phrase).nil?
   end
 end
diff --git a/spec/concepts/project/create_remix_spec.rb b/spec/concepts/project/create_remix_spec.rb
index 3c1307e1..058fe481 100644
--- a/spec/concepts/project/create_remix_spec.rb
+++ b/spec/concepts/project/create_remix_spec.rb
@@ -45,6 +45,11 @@
       expect(remixed_project.identifier).not_to eq(original_project.identifier)
     end
 
+    it 'sets new project locale to nil' do
+      remixed_project = create_remix[:project]
+      expect(remixed_project.locale).to be_nil
+    end
+
     it 'assigns user_id to new project' do
       remixed_project = create_remix[:project]
       expect(remixed_project.user_id).to eq(user_id)
diff --git a/spec/models/project_spec.rb b/spec/models/project_spec.rb
index 96f11a90..0572db25 100644
--- a/spec/models/project_spec.rb
+++ b/spec/models/project_spec.rb
@@ -14,6 +14,49 @@
     end
   end
 
+  describe 'validations' do
+    let(:project) { create(:project) }
+    let(:identifier) { project.identifier }
+
+    it 'is invalid if no user or locale' do
+      invalid_project = build(:project, locale: nil, user_id: nil)
+      expect(invalid_project).to be_invalid
+    end
+
+    it 'is valid if user but no locale' do
+      valid_project = build(:project, locale: nil)
+      expect(valid_project).to be_valid
+    end
+
+    context 'with same identifier and same user as existing project' do
+      let(:user_id) { project.user_id }
+
+      it 'is invalid if identifier in use by same user in the same locale' do
+        new_project = build(:project, identifier:, user_id:, locale: project.locale)
+        expect(new_project).to be_invalid
+      end
+
+      it 'is valid if identifier only in use by the user in the another locale' do
+        new_project = build(:project, identifier:, user_id:, locale: 'another_locale')
+        expect(new_project).to be_valid
+      end
+    end
+
+    context 'with same identifier but different user as existing project' do
+      let(:user_id) { 'another_user' }
+
+      it 'is invalid if identifier in use by another user in same locale' do
+        new_project = build(:project, identifier:, user_id:, locale: project.locale)
+        expect(new_project).to be_invalid
+      end
+
+      it 'is invalid if identifier in use in another locale by another user' do
+        new_project = build(:project, identifier:, user_id:, locale: 'another_locale')
+        expect(new_project).to be_invalid
+      end
+    end
+  end
+
   describe 'check_unique_not_null' do
     let(:saved_project) { create(:project) }
 
@@ -21,15 +64,5 @@
       unsaved_project = build(:project, identifier: nil)
       expect { unsaved_project.valid? }.to change { unsaved_project.identifier.nil? }.from(true).to(false)
     end
-
-    it 'generates identifier if non-unique within locale' do
-      invalid_project = build(:project, identifier: saved_project.identifier, locale: saved_project.locale)
-      expect { invalid_project.valid? }.to change(invalid_project, :identifier)
-    end
-
-    it 'does not change identifier if duplicated in different locale' do
-      valid_project = build(:project, identifier: saved_project.identifier, locale: 'ja-JP')
-      expect { valid_project.valid? }.not_to change(valid_project, :identifier)
-    end
   end
 end
diff --git a/spec/project_importer_spec.rb b/spec/project_importer_spec.rb
index 85a06554..0e6b0704 100644
--- a/spec/project_importer_spec.rb
+++ b/spec/project_importer_spec.rb
@@ -21,10 +21,10 @@
   end
 
   context 'when the project with correct locale does not already exist in the database' do
-    let(:project) { Project.find_by(identifier: importer.identifier, locale: importer.locale) }
+    let(:project) { Project.find_by(identifier: importer.identifier, user_id: nil, locale: importer.locale) }
 
     before do
-      create(:project, identifier: importer.identifier)
+      create(:project, identifier: importer.identifier, user_id: nil)
     end
 
     it 'saves the project to the database' do