--- a/layout/base/ServoRestyleManager.cpp
+++ b/layout/base/ServoRestyleManager.cpp
@@ -292,17 +292,18 @@ ServoRestyleManager::ContentStateChanged
 
 void
 ServoRestyleManager::AttributeWillChange(Element* aElement,
                                          int32_t aNameSpaceID,
                                          nsIAtom* aAttribute,
                                          int32_t aModType,
                                          const nsAttrValue* aNewValue)
 {
-  NS_ERROR("stylo: ServoRestyleManager::AttributeWillChange not implemented");
+  ServoElementSnapshot* snapshot = SnapshotForElement(aElement);
+  snapshot->AddAttrs(aElement);
 }
 
 void
 ServoRestyleManager::AttributeChanged(Element* aElement,
                                       int32_t aNameSpaceID,
                                       nsIAtom* aAttribute,
                                       int32_t aModType,
                                       const nsAttrValue* aOldValue)