--- a/layout/base/RestyleManager.cpp
+++ b/layout/base/RestyleManager.cpp
@@ -2587,16 +2587,18 @@ RestyleManager::ProcessPostTraversal(
   Element* aElement,
   ComputedStyle* aParentContext,
   ServoRestyleState& aRestyleState,
   ServoPostTraversalFlags aFlags)
 {
   nsIFrame* styleFrame = nsLayoutUtils::GetStyleFrame(aElement);
   nsIFrame* primaryFrame = aElement->GetPrimaryFrame();
 
+  MOZ_ASSERT(aElement->HasServoData(), "How in the world?");
+
   // NOTE(emilio): This is needed because for table frames the bit is set on the
   // table wrapper (which is the primary frame), not on the table itself.
   const bool isOutOfFlow =
     primaryFrame &&
     primaryFrame->HasAnyStateBits(NS_FRAME_OUT_OF_FLOW);
 
   // Grab the change hint from Servo.
   bool wasRestyled;