diff --git a/assets/javascripts/views/sidebar/doc_list.coffee b/assets/javascripts/views/sidebar/doc_list.coffee
index 21135972..0a8b2a5a 100644
--- a/assets/javascripts/views/sidebar/doc_list.coffee
+++ b/assets/javascripts/views/sidebar/doc_list.coffee
@@ -58,7 +58,7 @@ class app.views.DocList extends app.View
     docs = [].concat(app.disabledDocs.all()...)
 
     while doc = docs.shift()
-      if doc.version
+      if doc.version?
         versions = ''
         loop
           versions += @tmpl('sidebarDoc', doc, disabled: true)
diff --git a/assets/javascripts/views/sidebar/doc_picker.coffee b/assets/javascripts/views/sidebar/doc_picker.coffee
index 9cc73183..3dae5c51 100644
--- a/assets/javascripts/views/sidebar/doc_picker.coffee
+++ b/assets/javascripts/views/sidebar/doc_picker.coffee
@@ -34,7 +34,7 @@ class app.views.DocPicker extends app.View
     docs = app.docs.all().concat(app.disabledDocs.all()...)
 
     while doc = docs.shift()
-      if doc.version
+      if doc.version?
         [docs, versions] = @extractVersions(docs, doc)
         html += @tmpl('sidebarVersionedDoc', doc, @renderVersions(versions), open: app.docs.contains(doc))
       else
diff --git a/lib/docs/core/doc.rb b/lib/docs/core/doc.rb
index cf62ba56..52bb3a33 100644
--- a/lib/docs/core/doc.rb
+++ b/lib/docs/core/doc.rb
@@ -13,7 +13,7 @@ module Docs
       end
 
       def version(version = nil, &block)
-        return @version if version.nil?
+        return @version unless block_given?
 
         klass = Class.new(self)
         klass.class_exec(&block)
@@ -48,7 +48,7 @@ module Docs
 
       def slug
         slug = @slug || name.try(:downcase)
-        version? ? "#{slug}~#{version}" : slug
+        version? ? "#{slug}~#{version.downcase.gsub(/[^a-z0-9\_\.]/, '_')}" : slug
       end
 
       def path
@@ -66,7 +66,7 @@ module Docs
       def as_json
         json = { name: name, slug: slug, type: type }
         json[:links] = links if links.present?
-        json[:version] = version if version.present?
+        json[:version] = version if version.present? || defined?(@version)
         json[:release] = release if release.present?
         json
       end
diff --git a/test/lib/docs/core/doc_test.rb b/test/lib/docs/core/doc_test.rb
index d8ba011c..e836d42c 100644
--- a/test/lib/docs/core/doc_test.rb
+++ b/test/lib/docs/core/doc_test.rb
@@ -45,9 +45,9 @@ class DocsDocTest < MiniTest::Spec
       assert_equal 'doc', Docs::Doc.slug
     end
 
-    it "returns 'doc~42' when the class is Docs::Doc and its #version is '42'" do
-      stub(Docs::Doc).version { '42' }
-      assert_equal 'doc~42', Docs::Doc.slug
+    it "returns 'doc~4.2_lts' when the class is Docs::Doc and its #version is '42 LTS'" do
+      stub(Docs::Doc).version { '4.2 LTS' }
+      assert_equal 'doc~4.2_lts', Docs::Doc.slug
     end
 
     it "returns 'foo~42' when #slug has been set to 'foo' and #version to '42'" do
@@ -141,6 +141,12 @@ class DocsDocTest < MiniTest::Spec
         assert_equal attribute, doc.as_json[attribute.to_sym]
       end
     end
+
+    it "includes the doc's version when it's defined and nil" do
+      refute doc.as_json.key?(:version)
+      doc.version = nil
+      assert doc.as_json.key?(:version)
+    end
   end
 
   describe ".store_page" do