diff --git a/app/models/article.rb b/app/models/article.rb
index 29dff2879..bf5355371 100644
--- a/app/models/article.rb
+++ b/app/models/article.rb
@@ -24,7 +24,7 @@ class Article < ApplicationRecord
   has_many :rating_votes
   has_many :page_views
 
-  validates :slug, presence: { if: :published? }, format: /\A[0-9a-z-_]*\z/,
+  validates :slug, presence: { if: :published? }, format: /\A[0-9a-z\-_]*\z/,
                    uniqueness: { scope: :user_id }
   validates :title, presence: true,
                     length: { maximum: 128 }
diff --git a/spec/models/article_spec.rb b/spec/models/article_spec.rb
index 1e03a0769..2e13b9dca 100644
--- a/spec/models/article_spec.rb
+++ b/spec/models/article_spec.rb
@@ -111,7 +111,7 @@ RSpec.describe Article, type: :model do
     let(:article1) { build(:article, title: title, published: false) }
 
     before do
-      article0.validate
+      article0.validate!
     end
 
     context "when unpublished" do