diff --git a/js/src/gc/Cell.h b/js/src/gc/Cell.h
index d656b04f0b..fde676f5d3 100644
--- a/js/src/gc/Cell.h
+++ b/js/src/gc/Cell.h
@@ -261,14 +261,14 @@ Cell::needWriteBarrierPre(JS::Zone* zone) {
 /* static */ MOZ_ALWAYS_INLINE TenuredCell*
 TenuredCell::fromPointer(void* ptr)
 {
-    //MOZ_ASSERT(static_cast<TenuredCell*>(ptr)->isTenured());
+    MOZ_ASSERT(static_cast<TenuredCell*>(ptr)->isTenured());
     return static_cast<TenuredCell*>(ptr);
 }
 
 /* static */ MOZ_ALWAYS_INLINE const TenuredCell*
 TenuredCell::fromPointer(const void* ptr)
 {
-    //MOZ_ASSERT(static_cast<const TenuredCell*>(ptr)->isTenured());
+    MOZ_ASSERT(static_cast<const TenuredCell*>(ptr)->isTenured());
     return static_cast<const TenuredCell*>(ptr);
 }
 
diff --git a/js/src/gc/Marking.cpp b/js/src/gc/Marking.cpp
index 14657948eb..511d2b073b 100644
--- a/js/src/gc/Marking.cpp
+++ b/js/src/gc/Marking.cpp
@@ -1001,7 +1001,7 @@ bool
 js::GCMarker::mark(T* thing)
 {
     AssertShouldMarkInZone(thing);
-    //MOZ_ASSERT(!IsInsideNursery(TenuredCell::fromPointer(thing)));
+    MOZ_ASSERT(!IsInsideNursery(TenuredCell::fromPointer(thing)));
     return ParticipatesInCC<T>::value
            ? TenuredCell::fromPointer(thing)->markIfUnmarked(markColor())
            : TenuredCell::fromPointer(thing)->markIfUnmarked(MarkColor::Black);