--- a/js/src/gc/Nursery.cpp
+++ b/js/src/gc/Nursery.cpp
@@ -29,18 +29,16 @@ using namespace mozilla;
 bool
 js::Nursery::init()
 {
     JS_ASSERT(start() == 0);
 
     if (!hugeSlots.init())
         return false;
 
-    fallbackBitmap.clear(false);
-
     void *heap = MapAlignedPages(runtime(), NurserySize, Alignment);
 #ifdef JSGC_ROOT_ANALYSIS
     // Our poison pointers are not guaranteed to be invalid on 64-bit
     // architectures, and often are valid. We can't just reserve the full
     // poison range, because it might already have been taken up by something
     // else (shared library, previous allocation). So we'll just loop and
     // discard poison pointers until we get something valid.
     //
@@ -92,18 +90,16 @@ js::Nursery::disable()
     JS_ASSERT(position_ == start());
     numActiveChunks_ = 0;
     currentEnd_ = 0;
 }
 
 void *
 js::Nursery::allocate(size_t size)
 {
-    JS_ASSERT(size % ThingAlignment == 0);
-    JS_ASSERT(position() % ThingAlignment == 0);
     JS_ASSERT(!runtime()->isHeapBusy());
 
     if (position() + size > currentEnd()) {
         if (currentChunk_ + 1 == numActiveChunks_)
             return nullptr;
         setCurrentChunk(currentChunk_ + 1);
     }
 

--- a/js/src/gc/Nursery.h
+++ b/js/src/gc/Nursery.h
@@ -132,21 +132,16 @@ class Nursery
     /*
      * The set of externally malloced slots potentially kept live by objects
      * stored in the nursery. Any external slots that do not belong to a
      * tenured thing at the end of a minor GC must be freed.
      */
     typedef HashSet<HeapSlot *, PointerHasher<HeapSlot *, 3>, SystemAllocPolicy> HugeSlotsSet;
     HugeSlotsSet hugeSlots;
 
-    /* The marking bitmap for the fallback marker. */
-    static const size_t ThingAlignment = sizeof(JS::Value);
-    static const size_t FallbackBitmapBits = NurserySize / ThingAlignment;
-    BitArray<FallbackBitmapBits> fallbackBitmap;
-
 #ifdef DEBUG
     /*
      * In DEBUG builds, these bytes indicate the state of an unused segment of
      * nursery-allocated memory.
      */
     static const uint8_t FreshNursery = 0x2a;
     static const uint8_t SweptNursery = 0x2b;
     static const uint8_t AllocatedThing = 0x2c;