--- a/servo/components/style/gecko/snapshot.rs
+++ b/servo/components/style/gecko/snapshot.rs
@@ -143,35 +143,49 @@ impl ElementSnapshot for GeckoElementSna
         }
     }
 
     #[inline]
     fn has_attrs(&self) -> bool {
         self.has_any(Flags::Attributes)
     }
 
+    #[inline]
     fn id_attr(&self) -> Option<Atom> {
+        if !self.has_any(Flags::Id) {
+            return None
+        }
+
         let ptr = unsafe {
             bindings::Gecko_SnapshotAtomAttrValue(self,
                                                   atom!("id").as_ptr())
         };
 
         if ptr.is_null() {
             None
         } else {
             Some(Atom::from(ptr))
         }
     }
 
+    #[inline]
     fn has_class(&self, name: &Atom) -> bool {
-        snapshot_helpers::has_class(self.as_ptr(),
-                                    name,
-                                    bindings::Gecko_SnapshotClassOrClassList)
+        if self.has_any(Flags::MaybeClass) {
+            snapshot_helpers::has_class(self.as_ptr(),
+                                        name,
+                                        bindings::Gecko_SnapshotClassOrClassList)
+        } else {
+            false
+        }
     }
 
+    #[inline]
     fn each_class<F>(&self, callback: F)
         where F: FnMut(&Atom)
     {
+        if !self.has_any(Flags::MaybeClass) {
+            return;
+        }
         snapshot_helpers::each_class(self.as_ptr(),
                                      callback,
                                      bindings::Gecko_SnapshotClassOrClassList)
     }
 }