diff --git a/servo/components/script/dom/canvasgradient.rs b/servo/components/script/dom/canvasgradient.rs
index e25dc88ef725..eec31c3fc79a 100644
--- a/servo/components/script/dom/canvasgradient.rs
+++ b/servo/components/script/dom/canvasgradient.rs
@@ -44,7 +44,7 @@ impl CanvasGradient {
 
 impl<'a> CanvasGradientMethods for JSRef<'a, CanvasGradient> {
     // https://html.spec.whatwg.org/multipage/#dom-canvasgradient-addcolorstop
-    fn AddColorStop(self, offset: Finite<f32>, color: String) {
+    fn AddColorStop(self, offset: Finite<f64>, color: String) {
         let default_black = RGBA {
             red: 0.0,
             green: 0.0,
diff --git a/servo/components/script/dom/webidls/CanvasGradient.webidl b/servo/components/script/dom/webidls/CanvasGradient.webidl
index fbeab8439871..abe41d853dcb 100644
--- a/servo/components/script/dom/webidls/CanvasGradient.webidl
+++ b/servo/components/script/dom/webidls/CanvasGradient.webidl
@@ -3,10 +3,11 @@
  * 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/. */
 
+// https://html.spec.whatwg.org/#canvasgradient
+// [Exposed=(Window,Worker)]
 interface CanvasGradient {
   // opaque object
-  // addColorStop should take a double
-  void addColorStop(float offset, DOMString color);
+  void addColorStop(double offset, DOMString color);
 };