--- a/layout/base/ServoRestyleManager.cpp
+++ b/layout/base/ServoRestyleManager.cpp
@@ -1094,17 +1094,23 @@ ServoRestyleManager::SnapshotFor(Element
 }
 
 void
 ServoRestyleManager::DoProcessPendingRestyles(ServoTraversalFlags aFlags)
 {
   nsPresContext* presContext = PresContext();
 
   MOZ_ASSERT(presContext->Document(), "No document?  Pshaw!");
-  MOZ_ASSERT(!presContext->HasPendingMediaQueryUpdates(),
+  // FIXME(emilio): In the "flush animations" case, ideally, we should only
+  // recascade animation styles running on the compositor, so we shouldn't care
+  // about other styles, or new rules that apply to the page...
+  //
+  // However, that's not true as of right now, see bug 1388031 and bug 1388692.
+  MOZ_ASSERT((aFlags & ServoTraversalFlags::FlushThrottledAnimations) ||
+             !presContext->HasPendingMediaQueryUpdates(),
              "Someone forgot to update media queries?");
   MOZ_ASSERT(!nsContentUtils::IsSafeToRunScript(), "Missing a script blocker!");
   MOZ_ASSERT(!mInStyleRefresh, "Reentrant call?");
 
 
   if (MOZ_UNLIKELY(!presContext->PresShell()->DidInitialize())) {
     // PresShell::FlushPendingNotifications doesn't early-return in the case
     // where the PresShell hasn't yet been initialized (and therefore we haven't