diff --git a/js/src/debugger/Debugger-inl.h b/js/src/debugger/Debugger-inl.h
index 5b0fafb8ad77..ad12ea2f9a01 100644
--- a/js/src/debugger/Debugger-inl.h
+++ b/js/src/debugger/Debugger-inl.h
@@ -17,7 +17,8 @@
 /* static */ inline js::Debugger* js::Debugger::fromJSObject(
     const JSObject* obj) {
   MOZ_ASSERT(obj->is<DebuggerInstanceObject>());
-  return (Debugger*)obj->as<NativeObject>().getPrivate();
+  auto* dbg = &obj->as<DebuggerInstanceObject>();
+  return dbg->maybePtrFromReservedSlot<Debugger>(JSSLOT_DEBUG_DEBUGGER);
 }
 
 inline bool js::Debugger::isHookCallAllowed(JSContext* cx) const {
diff --git a/js/src/debugger/Debugger.cpp b/js/src/debugger/Debugger.cpp
index 47fe0b60dd1a..879eafd0f9d4 100644
--- a/js/src/debugger/Debugger.cpp
+++ b/js/src/debugger/Debugger.cpp
@@ -4015,9 +4015,7 @@ const JSClassOps DebuggerInstanceObject::classOps_ = {
 };
 
 const JSClass DebuggerInstanceObject::class_ = {
-    "Debugger",
-    JSCLASS_HAS_PRIVATE |
-        JSCLASS_HAS_RESERVED_SLOTS(Debugger::JSSLOT_DEBUG_COUNT),
+    "Debugger", JSCLASS_HAS_RESERVED_SLOTS(Debugger::JSSLOT_DEBUG_COUNT),
     &classOps_};
 
 static Debugger* Debugger_fromThisValue(JSContext* cx, const CallArgs& args,
@@ -4635,7 +4633,7 @@ bool Debugger::construct(JSContext* cx, unsigned argc, Value* vp) {
 
     // The object owns the released pointer.
     debugger = dbg.release();
-    InitObjectPrivate(obj, debugger, MemoryUse::Debugger);
+    InitReservedSlot(obj, JSSLOT_DEBUG_DEBUGGER, debugger, MemoryUse::Debugger);
   }
 
   // Add the initial debuggees, if any.
diff --git a/js/src/debugger/Debugger.h b/js/src/debugger/Debugger.h
index bc89e4bfb18f..c90eb564dbf6 100644
--- a/js/src/debugger/Debugger.h
+++ b/js/src/debugger/Debugger.h
@@ -541,6 +541,7 @@ class Debugger : private mozilla::LinkedListElement<Debugger> {
     HookCount
   };
   enum {
+    JSSLOT_DEBUG_DEBUGGER,
     JSSLOT_DEBUG_PROTO_START,
     JSSLOT_DEBUG_FRAME_PROTO = JSSLOT_DEBUG_PROTO_START,
     JSSLOT_DEBUG_ENV_PROTO,
diff --git a/js/src/vm/NativeObject.h b/js/src/vm/NativeObject.h
index 5c12cd860ec6..db541e4ea7a7 100644
--- a/js/src/vm/NativeObject.h
+++ b/js/src/vm/NativeObject.h
@@ -1179,6 +1179,12 @@ class NativeObject : public JSObject {
     fixedSlots()[slot].init(this, HeapSlot::Slot, slot, value);
   }
 
+  template <typename T>
+  T* maybePtrFromReservedSlot(uint32_t slot) const {
+    Value v = getReservedSlot(slot);
+    return v.isUndefined() ? nullptr : static_cast<T*>(v.toPrivate());
+  }
+
   /*
    * Calculate the number of dynamic slots to allocate to cover the properties
    * in an object with the given number of fixed slots and slot span.