diff --git a/js/src/gc/RootMarking.cpp b/js/src/gc/RootMarking.cpp
index 50bc98644ce3..7b9cf0db28a0 100644
--- a/js/src/gc/RootMarking.cpp
+++ b/js/src/gc/RootMarking.cpp
@@ -600,11 +600,11 @@ AutoHashableValueRooter::trace(JSTracer *trc)
 }
 
 void
-StackShape::AutoRooter::trace(JSTracer *trc)
+StackShape::trace(JSTracer *trc)
 {
-    if (shape->base)
-        MarkBaseShapeRoot(trc, (BaseShape**) &shape->base, "StackShape::AutoRooter base");
-    MarkIdRoot(trc, (jsid*) &shape->propid, "StackShape::AutoRooter id");
+    if (base)
+        MarkBaseShapeRoot(trc, (BaseShape**) &base, "StackShape base");
+    MarkIdRoot(trc, (jsid*) &propid, "StackShape id");
 }
 
 void
diff --git a/js/src/jsobj.cpp b/js/src/jsobj.cpp
index c52b69116e68..c14f37d0003f 100644
--- a/js/src/jsobj.cpp
+++ b/js/src/jsobj.cpp
@@ -1130,14 +1130,14 @@ JSObject::sealOrFreeze(JSContext *cx, HandleObject obj, ImmutabilityType it)
         Reverse(shapes.begin(), shapes.end());
 
         for (size_t i = 0; i < shapes.length(); i++) {
-            StackShape child(shapes[i]);
-            StackShape::AutoRooter rooter(cx, &child);
-            child.attrs |= getSealedOrFrozenAttributes(child.attrs, it);
+            StackShape unrootedChild(shapes[i]);
+            RootedGeneric<StackShape*> child(cx, &unrootedChild);
+            child->attrs |= getSealedOrFrozenAttributes(child->attrs, it);
 
-            if (!JSID_IS_EMPTY(child.propid) && it == FREEZE)
-                MarkTypePropertyNonWritable(cx, obj, child.propid);
+            if (!JSID_IS_EMPTY(child->propid) && it == FREEZE)
+                MarkTypePropertyNonWritable(cx, obj, child->propid);
 
-            last = cx->compartment()->propertyTree.getChild(cx, last, child);
+            last = cx->compartment()->propertyTree.getChild(cx, last, *child);
             if (!last)
                 return false;
         }
diff --git a/js/src/jspropertytree.cpp b/js/src/jspropertytree.cpp
index a35457d20b49..6e4d162576f4 100644
--- a/js/src/jspropertytree.cpp
+++ b/js/src/jspropertytree.cpp
@@ -126,7 +126,7 @@ Shape::removeChild(Shape *child)
 }
 
 Shape *
-PropertyTree::getChild(ExclusiveContext *cx, Shape *parentArg, const StackShape &child)
+PropertyTree::getChild(ExclusiveContext *cx, Shape *parentArg, StackShape &unrootedChild)
 {
     RootedShape parent(cx, parentArg);
     JS_ASSERT(parent);
@@ -144,11 +144,11 @@ PropertyTree::getChild(ExclusiveContext *cx, Shape *parentArg, const StackShape
     KidsPointer *kidp = &parent->kids;
     if (kidp->isShape()) {
         Shape *kid = kidp->toShape();
-        if (kid->matches(child))
-            existingShape = kid;
+        if (kid->matches(unrootedChild))
+        existingShape = kid;
     } else if (kidp->isHash()) {
-        if (KidsHash::Ptr p = kidp->toHash()->lookup(child))
-            existingShape = *p;
+        if (KidsHash::Ptr p = kidp->toHash()->lookup(unrootedChild))
+        existingShape = *p;
     } else {
         /* If kidp->isNull(), we always insert. */
     }
@@ -181,13 +181,13 @@ PropertyTree::getChild(ExclusiveContext *cx, Shape *parentArg, const StackShape
     if (existingShape)
         return existingShape;
 
-    StackShape::AutoRooter childRoot(cx, &child);
+    RootedGeneric<StackShape*> child(cx, &unrootedChild);
 
     Shape *shape = newShape(cx);
     if (!shape)
         return nullptr;
 
-    new (shape) Shape(child, parent->numFixedSlots());
+    new (shape) Shape(*child, parent->numFixedSlots());
 
     if (!insertChild(cx, parent, shape))
         return nullptr;
diff --git a/js/src/jspropertytree.h b/js/src/jspropertytree.h
index 1015bf4228b8..362c45c6d02c 100644
--- a/js/src/jspropertytree.h
+++ b/js/src/jspropertytree.h
@@ -97,7 +97,7 @@ class PropertyTree
     JSCompartment *compartment() { return compartment_; }
 
     Shape *newShape(ExclusiveContext *cx);
-    Shape *getChild(ExclusiveContext *cx, Shape *parent, const StackShape &child);
+    Shape *getChild(ExclusiveContext *cx, Shape *parent, StackShape &child);
     Shape *lookupChild(ThreadSafeContext *cx, Shape *parent, const StackShape &child);
 };
 
diff --git a/js/src/vm/Shape-inl.h b/js/src/vm/Shape-inl.h
index 4617d3395b90..c5fb04615429 100644
--- a/js/src/vm/Shape-inl.h
+++ b/js/src/vm/Shape-inl.h
@@ -234,14 +234,6 @@ AutoRooterGetterSetter::AutoRooterGetterSetter(ThreadSafeContext *cx, uint8_t at
     MOZ_GUARD_OBJECT_NOTIFIER_INIT;
 }
 
-inline
-StackShape::AutoRooter::AutoRooter(ThreadSafeContext *cx, const StackShape *shape_
-                                   MOZ_GUARD_OBJECT_NOTIFIER_PARAM_IN_IMPL)
-  : CustomAutoRooter(cx), shape(shape_), skip(cx, shape_)
-{
-    MOZ_GUARD_OBJECT_NOTIFIER_INIT;
-}
-
 } /* namespace js */
 
 #endif /* vm_Shape_inl_h */
diff --git a/js/src/vm/Shape.cpp b/js/src/vm/Shape.cpp
index 531bf1ad0065..73b92fa9f542 100644
--- a/js/src/vm/Shape.cpp
+++ b/js/src/vm/Shape.cpp
@@ -363,15 +363,15 @@ JSObject::getChildPropertyOnDictionary(ThreadSafeContext *cx, JS::HandleObject o
 
     if (obj->inDictionaryMode()) {
         JS_ASSERT(parent == obj->lastProperty());
-        StackShape::AutoRooter childRoot(cx, &child);
+        RootedGeneric<StackShape*> childRoot(cx, &child);
         shape = js_NewGCShape(cx);
         if (!shape)
             return nullptr;
-        if (child.hasSlot() && child.slot() >= obj->lastProperty()->base()->slotSpan()) {
-            if (!JSObject::setSlotSpan(cx, obj, child.slot() + 1))
+        if (childRoot->hasSlot() && childRoot->slot() >= obj->lastProperty()->base()->slotSpan()) {
+            if (!JSObject::setSlotSpan(cx, obj, childRoot->slot() + 1))
                 return nullptr;
         }
-        shape->initDictionaryShape(child, obj->numFixedSlots(), &obj->shape_);
+        shape->initDictionaryShape(*childRoot, obj->numFixedSlots(), &obj->shape_);
     }
 
     return shape;
@@ -379,13 +379,13 @@ JSObject::getChildPropertyOnDictionary(ThreadSafeContext *cx, JS::HandleObject o
 
 /* static */ Shape *
 JSObject::getChildProperty(ExclusiveContext *cx,
-                           HandleObject obj, HandleShape parent, StackShape &child)
+                           HandleObject obj, HandleShape parent, StackShape &unrootedChild)
 {
-    StackShape::AutoRooter childRoot(cx, &child);
-    RootedShape shape(cx, getChildPropertyOnDictionary(cx, obj, parent, child));
+    RootedGeneric<StackShape*> child(cx, &unrootedChild);
+    RootedShape shape(cx, getChildPropertyOnDictionary(cx, obj, parent, *child));
 
     if (!obj->inDictionaryMode()) {
-        shape = cx->compartment()->propertyTree.getChild(cx, parent, child);
+        shape = cx->compartment()->propertyTree.getChild(cx, parent, *child);
         if (!shape)
             return nullptr;
         //JS_ASSERT(shape->parent == parent);
@@ -399,15 +399,15 @@ JSObject::getChildProperty(ExclusiveContext *cx,
 
 /* static */ Shape *
 JSObject::lookupChildProperty(ThreadSafeContext *cx,
-                              HandleObject obj, HandleShape parent, StackShape &child)
+                              HandleObject obj, HandleShape parent, StackShape &unrootedChild)
 {
-    StackShape::AutoRooter childRoot(cx, &child);
+    RootedGeneric<StackShape*> child(cx, &unrootedChild);
     JS_ASSERT(cx->isThreadLocal(obj));
 
-    RootedShape shape(cx, getChildPropertyOnDictionary(cx, obj, parent, child));
+    RootedShape shape(cx, getChildPropertyOnDictionary(cx, obj, parent, *child));
 
     if (!obj->inDictionaryMode()) {
-        shape = cx->compartment_->propertyTree.lookupChild(cx, parent, child);
+        shape = cx->compartment_->propertyTree.lookupChild(cx, parent, *child);
         if (!shape)
             return nullptr;
         if (!JSObject::setLastProperty(cx, obj, shape))
diff --git a/js/src/vm/Shape.h b/js/src/vm/Shape.h
index 227b00f829b2..d1da317898c4 100644
--- a/js/src/vm/Shape.h
+++ b/js/src/vm/Shape.h
@@ -1546,19 +1546,9 @@ struct StackShape
         return hash;
     }
 
-    class AutoRooter : private JS::CustomAutoRooter
-    {
-      public:
-        inline AutoRooter(ThreadSafeContext *cx, const StackShape *shape_
-                          MOZ_GUARD_OBJECT_NOTIFIER_PARAM);
-
-      private:
-        virtual void trace(JSTracer *trc);
-
-        const StackShape *shape;
-        SkipRoot skip;
-        MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER
-    };
+    // For RootedGeneric<StackShape*>
+    static inline js::ThingRootKind rootKind() { return js::THING_ROOT_CUSTOM; }
+    void trace(JSTracer *trc);
 };
 
 } /* namespace js */