diff --git a/components/compositing/compositor.rs b/components/compositing/compositor.rs
index d964c0bdbee..304b523c87b 100644
--- a/components/compositing/compositor.rs
+++ b/components/compositing/compositor.rs
@@ -70,7 +70,7 @@ impl ConvertPipelineIdFromWebRender for webrender_api::PipelineId {
 
 /// Holds the state when running reftests that determines when it is
 /// safe to save the output image.
-#[derive(Clone, Copy, PartialEq)]
+#[derive(Clone, Copy, Debug, PartialEq)]
 enum ReadyState {
     Unknown,
     WaitingForConstellationReply,
@@ -495,7 +495,7 @@ impl<Window: WindowMethods> IOCompositor<Window> {
             }
 
             (Msg::IsReadyToSaveImageReply(is_ready), ShutdownState::NotShuttingDown) => {
-                assert!(self.ready_to_save_state == ReadyState::WaitingForConstellationReply);
+                assert_eq!(self.ready_to_save_state, ReadyState::WaitingForConstellationReply);
                 if is_ready {
                     self.ready_to_save_state = ReadyState::ReadyToSaveImage;
                     if opts::get().is_running_problem_test {