diff --git a/components/script/dom/event.rs b/components/script/dom/event.rs
index d45407a51fe..2cec78b48cc 100644
--- a/components/script/dom/event.rs
+++ b/components/script/dom/event.rs
@@ -19,7 +19,7 @@ use std::default::Default;
 
 use time;
 
-#[derive(JSTraceable, Copy, Clone)]
+#[derive(JSTraceable, Copy, Clone, Debug, PartialEq, Eq)]
 #[repr(u16)]
 #[derive(HeapSizeOf)]
 pub enum EventPhase {
@@ -136,6 +136,11 @@ impl Event {
         self.target.set(Some(JS::from_ref(val)));
     }
 
+    #[inline]
+    pub fn phase(&self) -> EventPhase {
+        self.phase.get()
+    }
+
     #[inline]
     pub fn set_phase(&self, val: EventPhase) {
         self.phase.set(val)
diff --git a/components/script/dom/eventdispatcher.rs b/components/script/dom/eventdispatcher.rs
index 3e1b9d83d7b..33c07c69bb0 100644
--- a/components/script/dom/eventdispatcher.rs
+++ b/components/script/dom/eventdispatcher.rs
@@ -91,6 +91,8 @@ pub fn dispatch_event(target: &EventTarget, pseudo_target: Option<&EventTarget>,
                       event: &Event) -> bool {
     assert!(!event.dispatching());
     assert!(event.initialized());
+    assert_eq!(event.phase(), EventPhase::None);
+    assert!(event.GetCurrentTarget().is_none());
 
     event.set_target(match pseudo_target {
         Some(pseudo_target) => pseudo_target,