--- a/js/src/gc/AllocKind.h
+++ b/js/src/gc/AllocKind.h
@@ -68,19 +68,17 @@ namespace gc {
     D(JITCODE,             JitCode,      js::jit::JitCode,  js::jit::JitCode,  false,  false) \
     D(SCOPE,               Scope,        js::Scope,         js::Scope,         true,   false) \
     D(REGEXP_SHARED,       RegExpShared, js::RegExpShared,  js::RegExpShared,  true,   false)
 
 #define FOR_EACH_ALLOCKIND(D) \
     FOR_EACH_OBJECT_ALLOCKIND(D) \
     FOR_EACH_NONOBJECT_ALLOCKIND(D)
 
-// FIXME: uint8_t would make more sense for the underlying type, but causes
-// miscompilations in GCC (fixed in 4.8.5 and 4.9.3). See also bug 1143966.
-enum class AllocKind {
+enum class AllocKind : uint8_t {
 #define DEFINE_ALLOC_KIND(allocKind, _1, _2, _3, _4, _5) allocKind,
 
     FOR_EACH_OBJECT_ALLOCKIND(DEFINE_ALLOC_KIND)
 
     OBJECT_LIMIT,
     OBJECT_LAST = OBJECT_LIMIT - 1,
 
     FOR_EACH_NONOBJECT_ALLOCKIND(DEFINE_ALLOC_KIND)

--- a/js/src/gc/Cell.h
+++ b/js/src/gc/Cell.h
@@ -37,17 +37,17 @@ CurrentThreadIsIonCompiling();
 #endif
 
 extern void
 TraceManuallyBarrieredGenericPointerEdge(JSTracer* trc, gc::Cell** thingp, const char* name);
 
 namespace gc {
 
 class Arena;
-enum class AllocKind;
+enum class AllocKind : uint8_t;
 struct Chunk;
 class TenuredCell;
 
 // A GC cell is the base class for all GC things.
 struct Cell
 {
   public:
     MOZ_ALWAYS_INLINE bool isTenured() const { return !IsInsideNursery(this); }

--- a/js/src/gc/Nursery.h
+++ b/js/src/gc/Nursery.h
@@ -60,17 +60,17 @@ class JSONPrinter;
 void SetGCZeal(JSRuntime*, uint8_t, uint32_t);
 
 namespace gc {
 class AutoMaybeStartBackgroundAllocation;
 struct Cell;
 class MinorCollectionTracer;
 class RelocationOverlay;
 struct TenureCountCache;
-enum class AllocKind;
+enum class AllocKind : uint8_t;
 class TenuredCell;
 } /* namespace gc */
 
 namespace jit {
 class MacroAssembler;
 } // namespace jit
 
 class TenuringTracer : public JSTracer