diff --git a/components/layout_thread/lib.rs b/components/layout_thread/lib.rs
index 403f30a96f5..958a2acc71e 100644
--- a/components/layout_thread/lib.rs
+++ b/components/layout_thread/lib.rs
@@ -674,8 +674,8 @@ impl LayoutThread {
                 let _rw_data = possibly_locked_rw_data.lock();
                 sender.send(self.epoch).unwrap();
             },
-            Msg::AdvanceClockMs(how_many) => {
-                self.handle_advance_clock_ms(how_many, possibly_locked_rw_data);
+            Msg::AdvanceClockMs(how_many, do_tick) => {
+                self.handle_advance_clock_ms(how_many, possibly_locked_rw_data, do_tick);
             }
             Msg::GetWebFontLoadState(sender) => {
                 let _rw_data = possibly_locked_rw_data.lock();
@@ -822,9 +822,12 @@ impl LayoutThread {
     /// Advances the animation clock of the document.
     fn handle_advance_clock_ms<'a, 'b>(&mut self,
                                        how_many_ms: i32,
-                                       possibly_locked_rw_data: &mut RwData<'a, 'b>) {
+                                       possibly_locked_rw_data: &mut RwData<'a, 'b>,
+                                       tick_animations: bool) {
         self.timer.increment(how_many_ms as f64 / 1000.0);
-        self.tick_all_animations(possibly_locked_rw_data);
+        if tick_animations {
+            self.tick_all_animations(possibly_locked_rw_data);
+        }
     }
 
     /// Sets quirks mode for the document, causing the quirks mode stylesheet to be used.
diff --git a/components/script/dom/testbinding.rs b/components/script/dom/testbinding.rs
index 13579d71330..372055483c7 100644
--- a/components/script/dom/testbinding.rs
+++ b/components/script/dom/testbinding.rs
@@ -613,8 +613,8 @@ impl TestBindingMethods for TestBinding {
         }
     }
 
-    fn AdvanceClock(&self, ms: i32) {
-        self.global().r().as_window().advance_animation_clock(ms);
+    fn AdvanceClock(&self, ms: i32, tick: bool) {
+        self.global().r().as_window().advance_animation_clock(ms, tick);
     }
 
     fn Panic(&self) { panic!("explicit panic from script") }
diff --git a/components/script/dom/webidls/TestBinding.webidl b/components/script/dom/webidls/TestBinding.webidl
index 9fc8a9e3bb6..9945f983ad7 100644
--- a/components/script/dom/webidls/TestBinding.webidl
+++ b/components/script/dom/webidls/TestBinding.webidl
@@ -439,7 +439,7 @@ interface TestBinding {
   [Pref="dom.testbinding.prefcontrolled.enabled"]
   const unsigned short prefControlledConstDisabled = 0;
   [Pref="layout.animations.test.enabled"]
-  void advanceClock(long millis);
+  void advanceClock(long millis, optional boolean forceLayoutTick = true);
 
   [Pref="dom.testbinding.prefcontrolled2.enabled"]
   readonly attribute boolean prefControlledAttributeEnabled;
diff --git a/components/script/dom/window.rs b/components/script/dom/window.rs
index c25c826b4ec..8aaa0adcde3 100644
--- a/components/script/dom/window.rs
+++ b/components/script/dom/window.rs
@@ -1074,9 +1074,9 @@ impl Window {
     }
 
     /// Advances the layout animation clock by `delta` milliseconds, and then
-    /// forces a reflow.
-    pub fn advance_animation_clock(&self, delta: i32) {
-        self.layout_chan.send(Msg::AdvanceClockMs(delta)).unwrap();
+    /// forces a reflow if `tick` is true.
+    pub fn advance_animation_clock(&self, delta: i32, tick: bool) {
+        self.layout_chan.send(Msg::AdvanceClockMs(delta, tick)).unwrap();
     }
 
     /// Reflows the page unconditionally if possible and not suppressed. This
diff --git a/components/script_layout_interface/message.rs b/components/script_layout_interface/message.rs
index b46703e778e..14580be4881 100644
--- a/components/script_layout_interface/message.rs
+++ b/components/script_layout_interface/message.rs
@@ -42,8 +42,9 @@ pub enum Msg {
 
     /// Updates layout's timer for animation testing from script.
     ///
-    /// The inner field is the number of *milliseconds* to advance.
-    AdvanceClockMs(i32),
+    /// The inner field is the number of *milliseconds* to advance, and the bool
+    /// field is whether animations should be force-ticked.
+    AdvanceClockMs(i32, bool),
 
     /// Requests that the layout thread reflow with a newly-loaded Web font.
     ReflowWithNewlyLoadedWebFont,