diff --git a/lib/docs/core/url.rb b/lib/docs/core/url.rb
index 511976e6..62b474e1 100644
--- a/lib/docs/core/url.rb
+++ b/lib/docs/core/url.rb
@@ -86,7 +86,7 @@ module Docs
     end
 
     def relative_path_to(url)
-      assert_absolute self, url = self.class.parse(url)
+      url = self.class.parse(url)
       return unless origin == url.origin
 
       base_dir = Pathname.new(normalized_path)
@@ -107,13 +107,5 @@ module Docs
     def relative_path_from(url)
       self.class.parse(url).relative_path_to(self)
     end
-
-    private
-
-    def assert_absolute(*args)
-      args.each do |url|
-        raise ArgumentError, "Expected absolute URL, got: #{url.to_s}" if url.relative?
-      end
-    end
   end
 end
diff --git a/test/lib/docs/core/url_test.rb b/test/lib/docs/core/url_test.rb
index 348ea94d..71464b9e 100644
--- a/test/lib/docs/core/url_test.rb
+++ b/test/lib/docs/core/url_test.rb
@@ -277,154 +277,161 @@ class DocsUrlTest < MiniTest::Spec
   end
 
   describe "#relative_path_to" do
-    context "when the URL is relative" do
+    context "when the URL is '/'" do
       let :url do
         URL.parse '/'
       end
 
-      it "raises an error with a relative url" do
-        assert_raises(ArgumentError) { url.relative_path_to '/' }
+      it "returns '.' with '/'" do
+        assert_equal '.', url.relative_path_to('/')
       end
 
-      it "raises an error with an absolute url" do
-        assert_raises(ArgumentError) { url.relative_path_to 'http://example.com' }
+      it "returns 'file' with '/file'" do
+        assert_equal 'file', url.relative_path_to('/file')
       end
-    end
 
-    context "when the URL is 'http://example.com'" do
-      let :url do
-        URL.parse 'http://example.com'
+      it "returns 'file/' with '/file/'" do
+        assert_equal 'file/', url.relative_path_to('/file/')
       end
 
-      it "raises an error with a relative url" do
-        assert_raises(ArgumentError) { url.relative_path_to '/' }
+      it "raises an error with 'file'" do
+        assert_raises ArgumentError do
+          url.relative_path_to 'file'
+        end
       end
+    end
 
-      it "returns '.' with 'http://example.com'" do
-        assert_equal '.', url.relative_path_to('http://example.com')
+    context "when the URL is '/path/to'" do
+      let :url do
+        URL.parse '/path/to'
       end
 
-      it "returns '.' with 'http://example.com/'" do
-        assert_equal '.', url.relative_path_to('http://example.com/')
+      it "returns '../' with '/'" do
+        assert_equal '../', url.relative_path_to('/')
       end
 
-      it "returns 'file' with 'http://example.com/file'" do
-        assert_equal 'file', url.relative_path_to('http://example.com/file')
+      it "returns '../path' with '/path'" do
+        assert_equal '../path', url.relative_path_to('/path')
       end
 
-      it "returns 'file/' with 'http://example.com/file/'" do
-        assert_equal 'file/', url.relative_path_to('http://example.com/file/')
+      it "returns '.' with '/path/'" do
+        assert_equal '.', url.relative_path_to('/path/')
       end
 
-      it "returns nil with 'https://example.com'" do
-        assert_nil url.relative_path_to('https://example.com')
+      it "returns 'to' with '/path/to'" do
+        assert_equal 'to', url.relative_path_to('/path/to')
       end
 
-      it "returns nil with 'http://not.example.com/file'" do
-        assert_nil url.relative_path_to('http://not.example.com/file')
+      it "returns '../PATH/to' with '/PATH/to'" do
+        assert_equal '../PATH/to', url.relative_path_to('/PATH/to')
       end
-    end
 
-    context "when the URL is 'http://example.com/'" do
-      let :url do
-        URL.parse 'http://example.com/'
+      it "returns 'to/' with '/path/to/'" do
+        assert_equal 'to/', url.relative_path_to('/path/to/')
       end
 
-      it "returns '.' with 'http://example.com'" do
-        assert_equal '.', url.relative_path_to('http://example.com')
+      it "returns 'to/file' with '/path/to/file'" do
+        assert_equal 'to/file', url.relative_path_to('/path/to/file')
       end
-    end
 
-    context "when the URL is 'http://example.com/path/to'" do
-      let :url do
-        URL.parse 'http://example.com/path/to'
+      it "returns 'to/file/' with '/path/to/file/'" do
+        assert_equal 'to/file/', url.relative_path_to('/path/to/file/')
       end
+    end
 
-      it "returns '../' with 'http://example.com'" do
-        assert_equal '../', url.relative_path_to('http://example.com')
+    context "when the URL is '/path/to/'" do
+      let :url do
+        URL.parse '/path/to/'
       end
 
-      it "returns '../' with 'http://example.com/'" do
-        assert_equal '../', url.relative_path_to('http://example.com/')
+      it "returns '../../' with ''" do
+        assert_equal '../../', url.relative_path_to('')
       end
 
-      it "returns '../path' with 'http://example.com/path'" do
-        assert_equal '../path', url.relative_path_to('http://example.com/path')
+      it "returns '../../' with '/'" do
+        assert_equal '../../', url.relative_path_to('/')
       end
 
-      it "returns '.' with 'http://example.com/path/'" do
-        assert_equal '.', url.relative_path_to('http://example.com/path/')
+      it "returns '../../path' with '/path'" do
+        assert_equal '../../path', url.relative_path_to('/path')
       end
 
-      it "returns 'to' with 'http://example.com/path/to'" do
-        assert_equal 'to', url.relative_path_to('http://example.com/path/to')
+      it "returns '../' with '/path/'" do
+        assert_equal '../', url.relative_path_to('/path/')
       end
 
-      it "returns '../PATH/to' with 'http://example.com/PATH/to'" do
-        assert_equal '../PATH/to', url.relative_path_to('http://example.com/PATH/to')
+      it "returns '../to' with '/path/to'" do
+        assert_equal '../to', url.relative_path_to('/path/to')
       end
 
-      it "returns 'to/' with 'http://example.com/path/to/'" do
-        assert_equal 'to/', url.relative_path_to('http://example.com/path/to/')
+      it "returns '.' with '/path/to/'" do
+        assert_equal '.', url.relative_path_to('/path/to/')
       end
 
-      it "returns 'to/file' with 'http://example.com/path/to/file'" do
-        assert_equal 'to/file', url.relative_path_to('http://example.com/path/to/file')
+      it "returns 'file' with '/path/to/file'" do
+        assert_equal 'file', url.relative_path_to('/path/to/file')
       end
 
-      it "returns 'to/file/' with 'http://example.com/path/to/file/'" do
-        assert_equal 'to/file/', url.relative_path_to('http://example.com/path/to/file/')
+      it "returns 'file/' with '/path/to/file/'" do
+        assert_equal 'file/', url.relative_path_to('/path/to/file/')
       end
     end
 
-    context "when the URL is 'http://example.com/path/to/'" do
+    context "when the URL is 'http://example.com'" do
       let :url do
-        URL.parse 'http://example.com/path/to/'
+        URL.parse 'http://example.com'
+      end
+
+      it "returns '.' with 'http://example.com'" do
+        assert_equal '.', url.relative_path_to('http://example.com')
       end
 
-      it "returns '../../' with 'http://example.com'" do
-        assert_equal '../../', url.relative_path_to('http://example.com')
+      it "returns '.' with 'http://example.com/'" do
+        assert_equal '.', url.relative_path_to('http://example.com/')
       end
 
-      it "returns '../../' with 'http://example.com/'" do
-        assert_equal '../../', url.relative_path_to('http://example.com/')
+      it "returns 'file' with 'http://example.com/file?query#frag'" do
+        assert_equal 'file', url.relative_path_to('http://example.com/file?query#frag')
       end
 
-      it "returns '../../path' with 'http://example.com/path'" do
-        assert_equal '../../path', url.relative_path_to('http://example.com/path')
+      it "returns nil with '/file'" do
+        assert_nil url.relative_path_to('/file')
       end
 
-      it "returns '../' with 'http://example.com/path/'" do
-        assert_equal '../', url.relative_path_to('http://example.com/path/')
+      it "returns nil with 'file'" do
+        assert_nil url.relative_path_to('file')
       end
 
-      it "returns '../to' with 'http://example.com/path/to'" do
-        assert_equal '../to', url.relative_path_to('http://example.com/path/to')
+      it "returns nil with 'https://example.com'" do
+        assert_nil url.relative_path_to('https://example.com')
       end
 
-      it "returns '.' with 'http://example.com/path/to/'" do
-        assert_equal '.', url.relative_path_to('http://example.com/path/to/')
+      it "returns nil with 'http://not.example.com/file'" do
+        assert_nil url.relative_path_to('http://not.example.com/file')
       end
+    end
 
-      it "returns 'file' with 'http://example.com/path/to/file'" do
-        assert_equal 'file', url.relative_path_to('http://example.com/path/to/file')
+    context "when the URL is 'http://example.com/'" do
+      let :url do
+        URL.parse 'http://example.com/'
       end
 
-      it "returns 'file/' with 'http://example.com/path/to/file/'" do
-        assert_equal 'file/', url.relative_path_to('http://example.com/path/to/file/')
+      it "returns '.' with 'http://example.com'" do
+        assert_equal '.', url.relative_path_to('http://example.com')
       end
     end
   end
 
   describe "#relative_path_from" do
-    context "when the URL is 'http://example.com/path/file'" do
-      let :url do
-        URL.parse 'http://example.com/path/file'
-      end
+    let :url do
+      URL.new
+    end
 
-      it "returns 'path/file' with 'http://example.com/path'" do
-        assert_equal 'path/file', url.relative_path_from('http://example.com/path')
+    it "returns the given url's #relative_path_to to self" do
+      any_instance_of URL do |instance|
+        stub(instance).relative_path_to(url) { 'path' }
       end
+      assert_equal 'path', url.relative_path_from('url')
     end
   end
 end