diff --git a/src/components/script/dom/bindings/codegen/CodegenRust.py b/src/components/script/dom/bindings/codegen/CodegenRust.py
index 4c28883ab13..13a03c91c08 100644
--- a/src/components/script/dom/bindings/codegen/CodegenRust.py
+++ b/src/components/script/dom/bindings/codegen/CodegenRust.py
@@ -4027,7 +4027,7 @@ def finalizeHook(descriptor, hookName, context):
         pass
     else:
         assert descriptor.nativeIsISupports
-        release = """let val = JS_GetReservedSlot(obj, 0);
+        release = """let val = JS_GetReservedSlot(obj, dom_object_slot(obj));
 let _: @mut %s = cast::transmute(RUST_JSVAL_TO_PRIVATE(val));
 debug!("%s finalize: %%p", this);
 """ % (descriptor.concreteType, descriptor.concreteType)
diff --git a/src/components/script/dom/bindings/utils.rs b/src/components/script/dom/bindings/utils.rs
index 6f931cc3290..bb405b3a473 100644
--- a/src/components/script/dom/bindings/utils.rs
+++ b/src/components/script/dom/bindings/utils.rs
@@ -121,14 +121,19 @@ pub fn is_dom_proxy(obj: *JSObject) -> bool {
 }
 
 #[fixed_stack_segment]
-pub unsafe fn unwrap<T>(obj: *JSObject) -> T {
+pub unsafe fn dom_object_slot(obj: *JSObject) -> u32 {
     let clasp = JS_GetClass(obj);
-    let slot = if is_dom_class(clasp) {
-        DOM_OBJECT_SLOT
+    if is_dom_class(clasp) {
+        DOM_OBJECT_SLOT as u32
     } else {
         assert!(is_dom_proxy(obj));
-        DOM_PROXY_OBJECT_SLOT
-    } as u32;
+        DOM_PROXY_OBJECT_SLOT as u32
+    }
+}
+
+#[fixed_stack_segment]
+pub unsafe fn unwrap<T>(obj: *JSObject) -> T {
+    let slot = dom_object_slot(obj);
     let val = JS_GetReservedSlot(obj, slot);
     cast::transmute(RUST_JSVAL_TO_PRIVATE(val))
 }