diff --git a/components/style/gecko/wrapper.rs b/components/style/gecko/wrapper.rs
index d399109fee8..5aa09092492 100644
--- a/components/style/gecko/wrapper.rs
+++ b/components/style/gecko/wrapper.rs
@@ -536,8 +536,9 @@ impl<'le> GeckoElement<'le> {
     fn get_extended_slots(
         &self,
     ) -> Option<&structs::FragmentOrElement_nsExtendedDOMSlots> {
-        self.get_dom_slots()
-            .and_then(|s| unsafe { s.mExtendedSlots.mPtr.as_ref() })
+        self.get_dom_slots().and_then(|s| unsafe {
+            (s._base.mExtendedSlots.mPtr as *const structs::FragmentOrElement_nsExtendedDOMSlots).as_ref()
+        })
     }
 
     #[inline]
@@ -592,7 +593,7 @@ impl<'le> GeckoElement<'le> {
     fn get_non_xul_xbl_binding_parent_raw_content(&self) -> *mut nsIContent {
         debug_assert!(!self.is_xul_element());
         self.get_extended_slots()
-            .map_or(ptr::null_mut(), |slots| slots.mBindingParent)
+            .map_or(ptr::null_mut(), |slots| slots._base.mBindingParent)
     }
 
     fn has_xbl_binding_parent(&self) -> bool {