diff --git a/app/models/tag.rb b/app/models/tag.rb
index a14e2cc98..0fa08e157 100644
--- a/app/models/tag.rb
+++ b/app/models/tag.rb
@@ -12,9 +12,10 @@
 class Tag < ApplicationRecord
   has_and_belongs_to_many :statuses
 
-  HASHTAG_RE = /(?:^|[^\/\)\w])#([[:word:]_]*[[:alpha:]_][[:word:]_]*)/i
+  HASHTAG_NAME_RE = '[[:word:]_]*[[:alpha:]_][[:word:]_]*'
+  HASHTAG_RE = /(?:^|[^\/\)\w])#(#{HASHTAG_NAME_RE})/i
 
-  validates :name, presence: true, uniqueness: true
+  validates :name, presence: true, uniqueness: true, format: { with: /\A#{HASHTAG_NAME_RE}\z/i }
 
   def to_param
     name
diff --git a/spec/models/tag_spec.rb b/spec/models/tag_spec.rb
index 555474c44..f727fa1dd 100644
--- a/spec/models/tag_spec.rb
+++ b/spec/models/tag_spec.rb
@@ -1,6 +1,24 @@
 require 'rails_helper'
 
 RSpec.describe Tag, type: :model do
+  describe 'validations' do
+    it 'invalid with #' do
+      expect(Tag.new(name: '#hello_world')).to_not be_valid
+    end
+
+    it 'invalid with .' do
+      expect(Tag.new(name: '.abcdef123')).to_not be_valid
+    end
+
+    it 'invalid with spaces' do
+      expect(Tag.new(name: 'hello world')).to_not be_valid
+    end
+
+    it 'valid with ａｅｓｔｈｅｔｉｃ' do
+      expect(Tag.new(name: 'ａｅｓｔｈｅｔｉｃ')).to be_valid
+    end
+  end
+
   describe 'HASHTAG_RE' do
     subject { Tag::HASHTAG_RE }