diff --git a/components/style/gecko_bindings/bindings.rs b/components/style/gecko_bindings/bindings.rs
index adeecc3925d..b3fa77ee974 100644
--- a/components/style/gecko_bindings/bindings.rs
+++ b/components/style/gecko_bindings/bindings.rs
@@ -927,6 +927,11 @@ extern "C" {
     pub fn Servo_DeclarationBlock_CreateEmpty()
      -> RawServoDeclarationBlockStrong;
 }
+extern "C" {
+    pub fn Servo_DeclarationBlock_Clone(declarations:
+                                            RawServoDeclarationBlockBorrowed)
+     -> RawServoDeclarationBlockStrong;
+}
 extern "C" {
     pub fn Servo_DeclarationBlock_Equals(a: RawServoDeclarationBlockBorrowed,
                                          b: RawServoDeclarationBlockBorrowed)
diff --git a/ports/geckolib/glue.rs b/ports/geckolib/glue.rs
index 4e3062faa0b..becd1ff7dc0 100644
--- a/ports/geckolib/glue.rs
+++ b/ports/geckolib/glue.rs
@@ -426,6 +426,13 @@ pub extern "C" fn Servo_DeclarationBlock_CreateEmpty() -> RawServoDeclarationBlo
     Arc::new(RwLock::new(PropertyDeclarationBlock { declarations: vec![], important_count: 0 })).into_strong()
 }
 
+#[no_mangle]
+pub extern "C" fn Servo_DeclarationBlock_Clone(declarations: RawServoDeclarationBlockBorrowed)
+                                               -> RawServoDeclarationBlockStrong {
+    let declarations = RwLock::<PropertyDeclarationBlock>::as_arc(&declarations);
+    Arc::new(RwLock::new(declarations.read().clone())).into_strong()
+}
+
 #[no_mangle]
 pub extern "C" fn Servo_DeclarationBlock_AddRef(declarations: RawServoDeclarationBlockBorrowed) {
     unsafe { RwLock::<PropertyDeclarationBlock>::addref(declarations) };