--- a/layout/style/ServoBindings.cpp
+++ b/layout/style/ServoBindings.cpp
@@ -441,38 +441,16 @@ Gecko_UnsetDirtyStyleAttr(RawGeckoElemen
     // XXX This can happen when nodes are adopted from a Gecko-style-backend
     //     document into a Servo-style-backend document.  See bug 1330051.
     NS_WARNING("stylo: requesting a Gecko declaration block?");
     return;
   }
   decl->UnsetDirty();
 }
 
-RawServoDeclarationBlockStrongBorrowedOrNull
-Gecko_GetSMILOverrideDeclarationBlock(RawGeckoElementBorrowed aElement)
-{
-  // This function duplicates a lot of the code in
-  // Gecko_GetStyleAttrDeclarationBlock above because I haven't worked out a way
-  // to persuade hazard analysis that a pointer-to-lambda is ok yet.
-  MOZ_ASSERT(aElement, "Invalid GeckoElement");
-
-  DeclarationBlock* decl =
-    const_cast<dom::Element*>(aElement)->GetSMILOverrideStyleDeclaration();
-  if (!decl) {
-    return nullptr;
-  }
-  if (decl->IsGecko()) {
-    // XXX This can happen when nodes are adopted from a Gecko-style-backend
-    //     document into a Servo-style-backend document.  See bug 1330051.
-    NS_WARNING("stylo: requesting a Gecko declaration block?");
-    return nullptr;
-  }
-  return decl->AsServo()->RefRawStrong();
-}
-
 const RawServoDeclarationBlockStrong*
 AsRefRawStrong(const RefPtr<RawServoDeclarationBlock>& aDecl)
 {
   static_assert(sizeof(RefPtr<RawServoDeclarationBlock>) ==
                 sizeof(RawServoDeclarationBlockStrong),
                 "RefPtr should just be a pointer");
   return reinterpret_cast<const RawServoDeclarationBlockStrong*>(&aDecl);
 }

--- a/layout/style/ServoBindings.h
+++ b/layout/style/ServoBindings.h
@@ -234,18 +234,16 @@ Gecko_GetActiveLinkAttrDeclarationBlock(
 // Returns whether private browsing is enabled for a given element.
 bool Gecko_IsPrivateBrowsingEnabled(const nsIDocument* aDoc);
 
 // Animations
 bool
 Gecko_GetAnimationRule(RawGeckoElementBorrowed aElementOrPseudo,
                        mozilla::EffectCompositor::CascadeLevel aCascadeLevel,
                        RawServoAnimationValueMapBorrowedMut aAnimationValues);
-RawServoDeclarationBlockStrongBorrowedOrNull
-Gecko_GetSMILOverrideDeclarationBlock(RawGeckoElementBorrowed element);
 bool Gecko_StyleAnimationsEquals(RawGeckoStyleAnimationListBorrowed,
                                  RawGeckoStyleAnimationListBorrowed);
 void Gecko_CopyAnimationNames(RawGeckoStyleAnimationListBorrowedMut aDest,
                               RawGeckoStyleAnimationListBorrowed aSrc);
 // This function takes an already addrefed nsAtom
 void Gecko_SetAnimationName(mozilla::StyleAnimation* aStyleAnimation,
                             nsAtom* aAtom);
 void Gecko_UpdateAnimations(RawGeckoElementBorrowed aElementOrPseudo,

--- a/layout/style/ServoBindings.toml
+++ b/layout/style/ServoBindings.toml
@@ -67,16 +67,17 @@ headers = [
     "mozilla/dom/Element.h",
     "mozilla/dom/ChildIterator.h",
     "mozilla/dom/NameSpaceConstants.h",
     "mozilla/LookAndFeel.h",
     "mozilla/StylePrefs.h",
     "mozilla/ServoBindings.h",
     "mozilla/ServoMediaList.h",
     "mozilla/ServoStyleContext.h",
+    "mozilla/ServoDeclarationBlock.h",
     "mozilla/SizeOfState.h",
     "nsCSSCounterStyleRule.h",
     "nsCSSFontFaceRule.h",
     "nsContentUtils.h",
     "nsNameSpaceManager.h",
     "nsMediaFeatures.h",
     "nsXBLBinding.h",
 ]
@@ -364,16 +365,17 @@ whitelist-types = [
     "StyleTransition",
     "ThemeWidgetType",
     "mozilla::UniquePtr",
     "mozilla::DefaultDelete",
     "mozilla::Side",
     "mozilla::binding_danger::AssertAndSuppressCleanupPolicy",
     "mozilla::ParsingMode",
     "mozilla::InheritTarget",
+    "mozilla::ServoDeclarationBlock",
     "mozilla::ServoMediaList",
     "mozilla::StyleRuleInclusion",
     "nsStyleTransformMatrix::MatrixTransformOperator",
 ]
 opaque-types = [
     "std::pair__PCCP",
     "std::namespace::atomic___base", "std::atomic__My_base",
     "std::atomic",

--- a/servo/components/style/gecko/wrapper.rs
+++ b/servo/components/style/gecko/wrapper.rs
@@ -37,17 +37,16 @@ use gecko_bindings::bindings::{Gecko_Set
 use gecko_bindings::bindings::Gecko_ClassOrClassList;
 use gecko_bindings::bindings::Gecko_ElementHasAnimations;
 use gecko_bindings::bindings::Gecko_ElementHasCSSAnimations;
 use gecko_bindings::bindings::Gecko_ElementHasCSSTransitions;
 use gecko_bindings::bindings::Gecko_GetActiveLinkAttrDeclarationBlock;
 use gecko_bindings::bindings::Gecko_GetAnimationRule;
 use gecko_bindings::bindings::Gecko_GetExtraContentStyleDeclarations;
 use gecko_bindings::bindings::Gecko_GetHTMLPresentationAttrDeclarationBlock;
-use gecko_bindings::bindings::Gecko_GetSMILOverrideDeclarationBlock;
 use gecko_bindings::bindings::Gecko_GetStyleAttrDeclarationBlock;
 use gecko_bindings::bindings::Gecko_GetUnvisitedLinkAttrDeclarationBlock;
 use gecko_bindings::bindings::Gecko_GetVisitedLinkAttrDeclarationBlock;
 use gecko_bindings::bindings::Gecko_IsSignificantChild;
 use gecko_bindings::bindings::Gecko_MatchLang;
 use gecko_bindings::bindings::Gecko_MatchStringArgPseudo;
 use gecko_bindings::bindings::Gecko_UnsetDirtyStyleAttr;
 use gecko_bindings::bindings::Gecko_UpdateAnimations;
@@ -1060,24 +1059,35 @@ impl<'le> TElement for GeckoElement<'le>
         if !self.may_have_style_attribute() {
             return;
         }
 
         unsafe { Gecko_UnsetDirtyStyleAttr(self.0) };
     }
 
     fn get_smil_override(&self) -> Option<ArcBorrow<Locked<PropertyDeclarationBlock>>> {
-        let declarations = unsafe { Gecko_GetSMILOverrideDeclarationBlock(self.0) };
-        let declarations: Option<&RawOffsetArc<Locked<PropertyDeclarationBlock>>> =
-            declarations.and_then(|s| s.as_arc_opt());
-        declarations.map(|s| s.borrow_arc())
+        unsafe {
+            let declaration: &structs::DeclarationBlock =
+                self.get_extended_slots()?.mSMILOverrideStyleDeclaration.mRawPtr.as_ref()?;
+
+            assert_eq!(declaration.mType, structs::StyleBackendType_Servo);
+            let declaration: &structs::ServoDeclarationBlock =
+                mem::transmute(declaration);
+
+            let raw: &structs::RawServoDeclarationBlock = declaration.mRaw.mRawPtr.as_ref()?;
+            Some(Locked::<PropertyDeclarationBlock>::as_arc(
+                &*(&raw as *const &structs::RawServoDeclarationBlock)
+            ).borrow_arc())
+        }
     }
 
-    fn get_animation_rule_by_cascade(&self, cascade_level: ServoCascadeLevel)
-                                     -> Option<Arc<Locked<PropertyDeclarationBlock>>> {
+    fn get_animation_rule_by_cascade(
+        &self,
+        cascade_level: ServoCascadeLevel,
+    ) -> Option<Arc<Locked<PropertyDeclarationBlock>>> {
         match cascade_level {
             ServoCascadeLevel::Animations => self.get_animation_rule(),
             ServoCascadeLevel::Transitions => self.get_transition_rule(),
             _ => panic!("Unsupported cascade level for getting the animation rule")
         }
     }
 
     fn get_animation_rule(