diff --git a/components/script/dom/document.rs b/components/script/dom/document.rs
index d60545e159b..2f0787ad6e4 100644
--- a/components/script/dom/document.rs
+++ b/components/script/dom/document.rs
@@ -23,6 +23,7 @@ use dom::bindings::codegen::InheritTypes::{HTMLAreaElementDerived, HTMLEmbedElem
 use dom::bindings::codegen::InheritTypes::{HTMLFormElementDerived, HTMLImageElementDerived};
 use dom::bindings::codegen::InheritTypes::{HTMLScriptElementDerived, HTMLTitleElementDerived};
 use dom::bindings::codegen::InheritTypes::ElementDerived;
+use dom::bindings::codegen::InheritTypes::HTMLBaseElementCast;
 use dom::bindings::codegen::UnionTypes::NodeOrString;
 use dom::bindings::error::{ErrorResult, Fallible};
 use dom::bindings::error::Error::{NotSupported, InvalidCharacter, Security};
@@ -45,6 +46,7 @@ use dom::element::{ElementTypeId, ActivationElementHelpers, FocusElementHelpers}
 use dom::event::{Event, EventBubbles, EventCancelable, EventHelpers};
 use dom::eventtarget::{EventTarget, EventTargetTypeId, EventTargetHelpers};
 use dom::htmlanchorelement::HTMLAnchorElement;
+use dom::htmlbaseelement::HTMLBaseElement;
 use dom::htmlcollection::{HTMLCollection, CollectionFilter};
 use dom::htmlelement::{HTMLElement, HTMLElementTypeId};
 use dom::htmlheadelement::HTMLHeadElement;
@@ -231,7 +233,14 @@ pub trait DocumentHelpers<'a> {
     fn encoding_name(self) -> Ref<'a, DOMString>;
     fn is_html_document(self) -> bool;
     fn is_fully_active(self) -> bool;
+    /// https://dom.spec.whatwg.org/#concept-document-url
     fn url(self) -> Url;
+    /// https://html.spec.whatwg.org/multipage/#fallback-base-url
+    fn fallback_base_url(self) -> Url;
+    /// https://html.spec.whatwg.org/multipage/#document-base-url
+    fn base_url(self) -> Url;
+    /// Returns the first `base` element in the DOM that has an `href` attribute.
+    fn base_element(self) -> Option<Root<HTMLBaseElement>>;
     fn quirks_mode(self) -> QuirksMode;
     fn set_quirks_mode(self, mode: QuirksMode);
     fn set_encoding_name(self, name: DOMString);
@@ -336,11 +345,38 @@ impl<'a> DocumentHelpers<'a> for &'a Document {
         true
     }
 
-    // https://dom.spec.whatwg.org/#dom-document-url
+    // https://dom.spec.whatwg.org/#concept-document-url
     fn url(self) -> Url {
         self.url.clone()
     }
 
+    // https://html.spec.whatwg.org/multipage/#fallback-base-url
+    fn fallback_base_url(self) -> Url {
+        // Step 1: iframe srcdoc (#4767).
+        // Step 2: about:blank with a creator browsing context.
+        // Step 3.
+        self.url()
+    }
+
+    // https://html.spec.whatwg.org/multipage/#document-base-url
+    fn base_url(self) -> Url {
+        match self.base_element() {
+            // Step 1.
+            None => self.fallback_base_url(),
+            // Step 2.
+            Some(base) => base.frozen_base_url(),
+        }
+    }
+
+    /// Returns the first `base` element in the DOM that has an `href` attribute.
+    fn base_element(self) -> Option<Root<HTMLBaseElement>> {
+        NodeCast::from_ref(self)
+            .traverse_preorder()
+            .filter_map(HTMLBaseElementCast::to_root)
+            .filter(|element| ElementCast::from_ref(&**element).has_attribute(&atom!("href")))
+            .next()
+    }
+
     fn quirks_mode(self) -> QuirksMode {
         self.quirks_mode.get()
     }
diff --git a/components/script/dom/htmlbaseelement.rs b/components/script/dom/htmlbaseelement.rs
index 6f4a585b113..42e7ffe6b5d 100644
--- a/components/script/dom/htmlbaseelement.rs
+++ b/components/script/dom/htmlbaseelement.rs
@@ -2,18 +2,22 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
+use dom::attr::AttrHelpers;
 use dom::bindings::codegen::Bindings::HTMLBaseElementBinding;
+use dom::bindings::codegen::InheritTypes::ElementCast;
 use dom::bindings::codegen::InheritTypes::HTMLBaseElementDerived;
 use dom::bindings::codegen::InheritTypes::HTMLElementCast;
 use dom::bindings::js::Root;
-use dom::document::Document;
+use dom::document::{Document, DocumentHelpers};
 use dom::eventtarget::{EventTarget, EventTargetTypeId};
-use dom::element::ElementTypeId;
+use dom::element::{ElementTypeId, AttributeHandlers};
 use dom::htmlelement::{HTMLElement, HTMLElementTypeId};
-use dom::node::{Node, NodeTypeId};
+use dom::node::{Node, NodeTypeId, document_from_node};
 use dom::virtualmethods::VirtualMethods;
 use util::str::DOMString;
 
+use url::{Url, UrlParser};
+
 #[dom_struct]
 pub struct HTMLBaseElement {
     htmlelement: HTMLElement
@@ -41,6 +45,16 @@ impl HTMLBaseElement {
         let element = HTMLBaseElement::new_inherited(localName, prefix, document);
         Node::reflect_node(box element, document, HTMLBaseElementBinding::Wrap)
     }
+
+    /// https://html.spec.whatwg.org/multipage/#frozen-base-url
+    pub fn frozen_base_url(&self) -> Url {
+        let href = ElementCast::from_ref(self).get_attribute(&ns!(""), &atom!("href"))
+            .expect("The frozen base url is only defined for base elements \
+                     that have a base url.");
+        let base = document_from_node(self).fallback_base_url();
+        let parsed = UrlParser::new().base_url(&base).parse(&href.value());
+        parsed.unwrap_or(base)
+    }
 }
 
 impl<'a> VirtualMethods for &'a HTMLBaseElement {