diff --git a/components/script/dom/htmlmediaelement.rs b/components/script/dom/htmlmediaelement.rs
index bcceffc11d4..13986728f32 100644
--- a/components/script/dom/htmlmediaelement.rs
+++ b/components/script/dom/htmlmediaelement.rs
@@ -85,7 +85,7 @@ pub struct HTMLMediaElement {
 /// https://html.spec.whatwg.org/multipage/#dom-media-networkstate
 #[derive(Clone, Copy, HeapSizeOf, JSTraceable, PartialEq)]
 #[repr(u8)]
-enum NetworkState {
+pub enum NetworkState {
     Empty = HTMLMediaElementConstants::NETWORK_EMPTY as u8,
     Idle = HTMLMediaElementConstants::NETWORK_IDLE as u8,
     Loading = HTMLMediaElementConstants::NETWORK_LOADING as u8,
@@ -443,12 +443,23 @@ impl HTMLMediaElement {
             #[allow(dead_code)]
             Object,
             Attribute(String),
-            // FIXME(nox): Support source element child.
-            #[allow(dead_code)]
             Children(Root<HTMLSourceElement>),
         }
-        let mode = if let Some(attr) = self.upcast::<Element>().get_attribute(&ns!(), &local_name!("src")) {
-            Mode::Attribute(attr.Value().into())
+        fn mode(media: &HTMLMediaElement) -> Option<Mode> {
+            if let Some(attr) = media.upcast::<Element>().get_attribute(&ns!(), &local_name!("src")) {
+                return Some(Mode::Attribute(attr.Value().into()));
+            }
+            let source_child_element = media.upcast::<Node>()
+                .children()
+                .filter_map(Root::downcast::<HTMLSourceElement>)
+                .next();
+            if let Some(element) = source_child_element {
+                return Some(Mode::Children(element));
+            }
+            None
+        }
+        let mode = if let Some(mode) = mode(self) {
+            mode
         } else {
             self.network_state.set(NetworkState::Empty);
             return;
@@ -775,6 +786,19 @@ impl HTMLMediaElement {
             }
         }
     }
+
+    /// Handles insertion of `source` children.
+    ///
+    /// https://html.spec.whatwg.org/multipage/#the-source-element:nodes-are-inserted
+    pub fn handle_source_child_insertion(&self) {
+        if self.upcast::<Element>().has_attribute(&local_name!("src")) {
+            return;
+        }
+        if self.network_state.get() != NetworkState::Empty {
+            return;
+        }
+        self.media_element_load_algorithm();
+    }
 }
 
 impl HTMLMediaElementMethods for HTMLMediaElement {
diff --git a/components/script/dom/htmlsourceelement.rs b/components/script/dom/htmlsourceelement.rs
index 84adbc16548..865b21d6acb 100644
--- a/components/script/dom/htmlsourceelement.rs
+++ b/components/script/dom/htmlsourceelement.rs
@@ -3,10 +3,14 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 use dom::bindings::codegen::Bindings::HTMLSourceElementBinding;
+use dom::bindings::codegen::Bindings::NodeBinding::NodeBinding::NodeMethods;
+use dom::bindings::inheritance::Castable;
 use dom::bindings::js::Root;
 use dom::document::Document;
 use dom::htmlelement::HTMLElement;
+use dom::htmlmediaelement::HTMLMediaElement;
 use dom::node::Node;
+use dom::virtualmethods::VirtualMethods;
 use dom_struct::dom_struct;
 use html5ever::{LocalName, Prefix};
 
@@ -34,3 +38,18 @@ impl HTMLSourceElement {
                            HTMLSourceElementBinding::Wrap)
     }
 }
+
+impl VirtualMethods for HTMLSourceElement {
+    fn super_type(&self) -> Option<&VirtualMethods> {
+        Some(self.upcast::<HTMLElement>() as &VirtualMethods)
+    }
+
+    /// https://html.spec.whatwg.org/multipage/#the-source-element:nodes-are-inserted
+    fn bind_to_tree(&self, tree_in_doc: bool) {
+        self.super_type().unwrap().bind_to_tree(tree_in_doc);
+        let parent = self.upcast::<Node>().GetParentNode().unwrap();
+        if let Some(media) = parent.downcast::<HTMLMediaElement>() {
+            media.handle_source_child_insertion();
+        }
+    }
+}
diff --git a/components/script/dom/virtualmethods.rs b/components/script/dom/virtualmethods.rs
index 2e4376ab975..b9adcea198e 100644
--- a/components/script/dom/virtualmethods.rs
+++ b/components/script/dom/virtualmethods.rs
@@ -41,6 +41,7 @@ use dom::htmloptionelement::HTMLOptionElement;
 use dom::htmloutputelement::HTMLOutputElement;
 use dom::htmlscriptelement::HTMLScriptElement;
 use dom::htmlselectelement::HTMLSelectElement;
+use dom::htmlsourceelement::HTMLSourceElement;
 use dom::htmlstyleelement::HTMLStyleElement;
 use dom::htmltablecellelement::HTMLTableCellElement;
 use dom::htmltableelement::HTMLTableElement;
@@ -231,6 +232,9 @@ pub fn vtable_for(node: &Node) -> &VirtualMethods {
         NodeTypeId::Element(ElementTypeId::HTMLElement(HTMLElementTypeId::HTMLSelectElement)) => {
             node.downcast::<HTMLSelectElement>().unwrap() as &VirtualMethods
         }
+        NodeTypeId::Element(ElementTypeId::HTMLElement(HTMLElementTypeId::HTMLSourceElement)) => {
+            node.downcast::<HTMLSourceElement>().unwrap() as &VirtualMethods
+        }
         NodeTypeId::Element(ElementTypeId::HTMLElement(HTMLElementTypeId::HTMLStyleElement)) => {
             node.downcast::<HTMLStyleElement>().unwrap() as &VirtualMethods
         }
diff --git a/tests/wpt/metadata/html/semantics/embedded-content/media-elements/loading-the-media-resource/load-removes-queued-error-event.html.ini b/tests/wpt/metadata/html/semantics/embedded-content/media-elements/loading-the-media-resource/load-removes-queued-error-event.html.ini
index 731fe16fc1b..c19f8ec60ce 100644
--- a/tests/wpt/metadata/html/semantics/embedded-content/media-elements/loading-the-media-resource/load-removes-queued-error-event.html.ini
+++ b/tests/wpt/metadata/html/semantics/embedded-content/media-elements/loading-the-media-resource/load-removes-queued-error-event.html.ini
@@ -1,6 +1,5 @@
 [load-removes-queued-error-event.html]
   type: testharness
-  expected: TIMEOUT
   [source error event]
-    expected: TIMEOUT
+    expected: FAIL
 
diff --git a/tests/wpt/metadata/html/semantics/embedded-content/media-elements/loading-the-media-resource/resource-selection-candidate-insert-before.html.ini b/tests/wpt/metadata/html/semantics/embedded-content/media-elements/loading-the-media-resource/resource-selection-candidate-insert-before.html.ini
index 4908ff33efe..76c0a336069 100644
--- a/tests/wpt/metadata/html/semantics/embedded-content/media-elements/loading-the-media-resource/resource-selection-candidate-insert-before.html.ini
+++ b/tests/wpt/metadata/html/semantics/embedded-content/media-elements/loading-the-media-resource/resource-selection-candidate-insert-before.html.ini
@@ -1,6 +1,5 @@
 [resource-selection-candidate-insert-before.html]
   type: testharness
-  expected: TIMEOUT
   [inserting another source before the candidate]
-    expected: TIMEOUT
+    expected: FAIL
 
diff --git a/tests/wpt/metadata/html/semantics/embedded-content/media-elements/loading-the-media-resource/resource-selection-invoke-insert-source-not-in-document.html.ini b/tests/wpt/metadata/html/semantics/embedded-content/media-elements/loading-the-media-resource/resource-selection-invoke-insert-source-not-in-document.html.ini
deleted file mode 100644
index d6c3a5c9926..00000000000
--- a/tests/wpt/metadata/html/semantics/embedded-content/media-elements/loading-the-media-resource/resource-selection-invoke-insert-source-not-in-document.html.ini
+++ /dev/null
@@ -1,5 +0,0 @@
-[resource-selection-invoke-insert-source-not-in-document.html]
-  type: testharness
-  [invoking resource selection by inserting <source> in video not in a document]
-    expected: FAIL
-
diff --git a/tests/wpt/metadata/html/semantics/embedded-content/media-elements/loading-the-media-resource/resource-selection-invoke-insert-source.html.ini b/tests/wpt/metadata/html/semantics/embedded-content/media-elements/loading-the-media-resource/resource-selection-invoke-insert-source.html.ini
deleted file mode 100644
index e7fd87a4aa0..00000000000
--- a/tests/wpt/metadata/html/semantics/embedded-content/media-elements/loading-the-media-resource/resource-selection-invoke-insert-source.html.ini
+++ /dev/null
@@ -1,5 +0,0 @@
-[resource-selection-invoke-insert-source.html]
-  type: testharness
-  [invoking resource selection by inserting <source>]
-    expected: FAIL
-
diff --git a/tests/wpt/metadata/html/semantics/embedded-content/media-elements/loading-the-media-resource/resource-selection-remove-source.html.ini b/tests/wpt/metadata/html/semantics/embedded-content/media-elements/loading-the-media-resource/resource-selection-remove-source.html.ini
deleted file mode 100644
index d827b0ad685..00000000000
--- a/tests/wpt/metadata/html/semantics/embedded-content/media-elements/loading-the-media-resource/resource-selection-remove-source.html.ini
+++ /dev/null
@@ -1,5 +0,0 @@
-[resource-selection-remove-source.html]
-  type: testharness
-  [Changes to networkState when inserting and removing a <source>]
-    expected: FAIL
-