diff --git a/app/models/category.rb b/app/models/category.rb
index 971d5d0fb58..d52a6941d25 100644
--- a/app/models/category.rb
+++ b/app/models/category.rb
@@ -85,6 +85,11 @@ class Category < ActiveRecord::Base
     if name.present?
       self.slug = Slug.for(name)
 
+      # Reject slugs that only contain numbers, because that's indistinguishable from an id.
+      self.slug = '' unless self.slug =~ /[^\d]/
+
+      return if self.slug.blank?
+
       # If a category with that slug already exists, set the slug to nil so the category can be found
       # another way.
       category = Category.where(slug: self.slug)
diff --git a/spec/models/category_spec.rb b/spec/models/category_spec.rb
index cb4f937bee8..0c3f8d12e6b 100644
--- a/spec/models/category_spec.rb
+++ b/spec/models/category_spec.rb
@@ -104,6 +104,14 @@ describe Category do
     end
   end
 
+  describe 'slug would be a number' do
+    let(:category) { Fabricate(:category, name: "電車男 2") }
+
+    it 'creates a blank slug' do
+      category.slug.should be_blank
+    end
+  end
+
   describe 'after create' do
     before do
       @category = Fabricate(:category, name: 'Amazing Category')