diff --git a/Gemfile b/Gemfile
index 5aad2c4d..dfbbdfd9 100644
--- a/Gemfile
+++ b/Gemfile
@@ -22,6 +22,7 @@ group :test do
   gem "rspec-mocks"
   gem "nokogiri"
   gem "rspec"
+  gem "test-theme", path: File.expand_path("./test/fixtures/test-theme", File.dirname(__FILE__))
 end
 
 #
diff --git a/lib/jekyll/theme.rb b/lib/jekyll/theme.rb
index 45a9aa3c..13bed36c 100644
--- a/lib/jekyll/theme.rb
+++ b/lib/jekyll/theme.rb
@@ -4,11 +4,11 @@ module Jekyll
 
     def initialize(name)
       @name = name.downcase.strip
-      raise MissingDependencyException unless gemspec
+      raise Jekyll::Errors::MissingDependencyException unless gemspec
     end
 
     def root
-      @root ||= gemspec.gem_dir
+      @root ||= gemspec.full_gem_path
     end
 
     def version
@@ -34,7 +34,8 @@ module Jekyll
     private
 
     def path_for(folder)
-      Jekyll.sanitized_path root, "_#{folder}"
+      path = Jekyll.sanitized_path root, "_#{folder}"
+      path if Dir.exists?(path)
     end
 
     def gemspec
diff --git a/test/fixtures/test-theme/_assets/application.coffee b/test/fixtures/test-theme/_assets/application.coffee
new file mode 100644
index 00000000..e69de29b
diff --git a/test/fixtures/test-theme/_assets/script.js b/test/fixtures/test-theme/_assets/script.js
new file mode 100644
index 00000000..e69de29b
diff --git a/test/fixtures/test-theme/_includes/include.html b/test/fixtures/test-theme/_includes/include.html
new file mode 100644
index 00000000..e69de29b
diff --git a/test/fixtures/test-theme/_layouts/default.html b/test/fixtures/test-theme/_layouts/default.html
new file mode 100644
index 00000000..e69de29b
diff --git a/test/fixtures/test-theme/_sass/style.scss b/test/fixtures/test-theme/_sass/style.scss
new file mode 100644
index 00000000..e69de29b
diff --git a/test/fixtures/test-theme/test-theme.gemspec b/test/fixtures/test-theme/test-theme.gemspec
new file mode 100644
index 00000000..5f950ae1
--- /dev/null
+++ b/test/fixtures/test-theme/test-theme.gemspec
@@ -0,0 +1,9 @@
+Gem::Specification.new do |s|
+  s.name        = 'test-theme'
+  s.version     = '0.1.0'
+  s.licenses    = ['MIT']
+  s.summary     = "This is a theme used to test Jekyll"
+  s.authors     = ["Jekyll"]
+  s.files       = ["lib/example.rb"]
+  s.homepage    = 'https://github.com/jekyll/jekyll'
+end
diff --git a/test/test_theme.rb b/test/test_theme.rb
new file mode 100644
index 00000000..e996ac6f
--- /dev/null
+++ b/test/test_theme.rb
@@ -0,0 +1,55 @@
+require 'helper'
+
+class TestTheme < JekyllUnitTest
+  def setup
+    @theme = Theme.new('test-theme')
+    @expected_root = File.expand_path "./fixtures/test-theme", File.dirname(__FILE__)
+  end
+
+  context "initializing" do
+    should "normalize the theme name" do
+      theme = Theme.new(' Test-Theme ')
+      assert_equal "test-theme", theme.name
+    end
+
+    should "know the theme root" do
+      assert_equal @expected_root, @theme.root
+    end
+
+    should "know the theme version" do
+      assert_equal Gem::Version.new("0.1.0"), @theme.version
+    end
+
+    should "raise an error for invalid themes" do
+      assert_raises Jekyll::Errors::MissingDependencyException do
+        Theme.new("foo")
+      end
+    end
+  end
+
+  context "path generation" do
+    ["assets", "layouts", "includes", "sass"].each do |folder|
+      should "know the #{folder} path" do
+        expected = File.expand_path("_#{folder}", @expected_root)
+        assert_equal expected, @theme.public_send("#{folder}_path")
+      end
+    end
+
+    should "generate folder paths" do
+      expected = File.expand_path("_assets", @expected_root)
+      assert_equal expected, @theme.send(:path_for, "assets")
+    end
+
+    should "not allow paths outside of the theme root" do
+      assert_equal nil, @theme.send(:path_for, "../../source")
+    end
+
+    should "return nil for paths that don't exist" do
+      assert_equal nil, @theme.send(:path_for, "foo")
+    end
+  end
+
+  should "retrieve the gemspec" do
+    assert_equal "test-theme-0.1.0", @theme.send(:gemspec).full_name
+  end
+end