diff --git a/components/layout/query.rs b/components/layout/query.rs
index 348a3ad556d..54acfe92e90 100644
--- a/components/layout/query.rs
+++ b/components/layout/query.rs
@@ -107,11 +107,8 @@ impl LayoutRPC for LayoutRPCImpl {
         if mouse_over_list.is_empty() {
             Err(())
         } else {
-            let response_list =
-                mouse_over_list.iter()
-                               .map(|metadata| metadata.node.to_untrusted_node_address())
-                               .collect();
-            Ok(MouseOverResponse(response_list))
+            let response = mouse_over_list[0].node.to_untrusted_node_address();
+            Ok(MouseOverResponse(response))
         }
     }
 
diff --git a/components/script/dom/document.rs b/components/script/dom/document.rs
index 501ad242305..4062fb7415f 100644
--- a/components/script/dom/document.rs
+++ b/components/script/dom/document.rs
@@ -574,11 +574,11 @@ impl Document {
         }
     }
 
-    pub fn get_nodes_under_mouse(&self, page_point: &Point2D<f32>) -> Vec<UntrustedNodeAddress> {
+    pub fn get_node_under_mouse(&self, page_point: &Point2D<f32>) -> Option<UntrustedNodeAddress> {
         assert!(self.GetDocumentElement().is_some());
         match self.window.layout().mouse_over(*page_point) {
-            Ok(MouseOverResponse(node_address)) => node_address,
-            Err(()) => vec![],
+            Ok(MouseOverResponse(node_address)) => Some(node_address),
+            Err(()) => None,
         }
     }
 
@@ -808,18 +808,21 @@ impl Document {
                                    client_point: Option<Point2D<f32>>,
                                    prev_mouse_over_targets: &mut RootedVec<JS<Element>>) {
         // Build a list of elements that are currently under the mouse.
-        let mouse_over_addresses = client_point.as_ref().map(|client_point| {
+        let mouse_over_address = client_point.as_ref().map(|client_point| {
             let page_point = Point2D::new(client_point.x + self.window.PageXOffset() as f32,
                                           client_point.y + self.window.PageYOffset() as f32);
-            self.get_nodes_under_mouse(&page_point)
-        }).unwrap_or(vec![]);
-        let mut mouse_over_targets = mouse_over_addresses.iter().map(|node_address| {
-            node::from_untrusted_node_address(js_runtime, *node_address)
-                .inclusive_ancestors()
-                .filter_map(Root::downcast::<Element>)
-                .next()
-                .unwrap()
-        }).collect::<RootedVec<JS<Element>>>();
+            self.get_node_under_mouse(&page_point)
+        }).unwrap_or(None);
+
+        let mut mouse_over_targets = RootedVec::<JS<Element>>::new();
+
+        if let Some(address) = mouse_over_address {
+            let node = node::from_untrusted_node_address(js_runtime, address);
+            for node in node.inclusive_ancestors()
+                            .filter_map(Root::downcast::<Element>) {
+                mouse_over_targets.push(JS::from_rooted(&node));
+            }
+        }
 
         // Remove hover from any elements in the previous list that are no longer
         // under the mouse.
@@ -856,9 +859,9 @@ impl Document {
         }
 
         // Send mousemove event to topmost target
-        if mouse_over_addresses.len() > 0 {
+        if let Some(address) = mouse_over_address {
             let top_most_node = node::from_untrusted_node_address(js_runtime,
-                                                                  mouse_over_addresses[0]);
+                                                                  address);
             let client_point = client_point.unwrap(); // Must succeed because hit test succeeded.
 
             // If the target is an iframe, forward the event to the child document.
diff --git a/components/script/layout_interface.rs b/components/script/layout_interface.rs
index 17f553d43e8..4ad7c241f14 100644
--- a/components/script/layout_interface.rs
+++ b/components/script/layout_interface.rs
@@ -106,6 +106,7 @@ pub trait LayoutRPC {
     fn node_geometry(&self) -> NodeGeometryResponse;
     /// Requests the node containing the point of interest
     fn hit_test(&self, point: Point2D<f32>) -> Result<HitTestResponse, ()>;
+    /// Query layout for the topmost node under the mouse.
     fn mouse_over(&self, point: Point2D<f32>) -> Result<MouseOverResponse, ()>;
     /// Query layout for the resolved value of a given CSS property
     fn resolved_style(&self) -> ResolvedStyleResponse;
@@ -139,7 +140,7 @@ pub struct NodeGeometryResponse {
     pub client_rect: Rect<i32>,
 }
 pub struct HitTestResponse(pub UntrustedNodeAddress);
-pub struct MouseOverResponse(pub Vec<UntrustedNodeAddress>);
+pub struct MouseOverResponse(pub UntrustedNodeAddress);
 pub struct ResolvedStyleResponse(pub Option<String>);
 
 #[derive(Clone)]