diff --git a/js/src/jsgc.cpp b/js/src/jsgc.cpp
index aedbcfec24a8..73bb5d6494eb 100644
--- a/js/src/jsgc.cpp
+++ b/js/src/jsgc.cpp
@@ -494,19 +494,19 @@ AllocateArena(JSContext *cx, unsigned thingKind)
 }
 
 JS_FRIEND_API(bool)
-IsAboutToBeFinalized(JSContext *cx, void *thing)
+IsAboutToBeFinalized(JSContext *cx, const void *thing)
 {
     if (JSAtom::isStatic(thing))
         return false;
     JS_ASSERT(cx);
 
-    JSCompartment *thingCompartment = reinterpret_cast<Cell *>(thing)->compartment();
+    JSCompartment *thingCompartment = reinterpret_cast<const Cell *>(thing)->compartment();
     JSRuntime *rt = cx->runtime;
     JS_ASSERT(rt == thingCompartment->rt);
     if (rt->gcCurrentCompartment != NULL && rt->gcCurrentCompartment != thingCompartment)
         return false;
 
-    return !reinterpret_cast<Cell *>(thing)->isMarked();
+    return !reinterpret_cast<const Cell *>(thing)->isMarked();
 }
 
 JS_FRIEND_API(bool)
@@ -1317,9 +1317,9 @@ GCMarker::~GCMarker()
 }
 
 void
-GCMarker::delayMarkingChildren(void *thing)
+GCMarker::delayMarkingChildren(const void *thing)
 {
-    Cell *cell = reinterpret_cast<Cell *>(thing);
+    const Cell *cell = reinterpret_cast<const Cell *>(thing);
     Arena<Cell> *a = cell->arena();
     JS_ASSERT(cell->isMarked());
     METER(cell->compartment()->rt->gcStats.unmarked++);
diff --git a/js/src/jsgc.h b/js/src/jsgc.h
index 7c5fb79bc13c..6247be0c9fb2 100644
--- a/js/src/jsgc.h
+++ b/js/src/jsgc.h
@@ -163,7 +163,7 @@ struct Arena {
     inline ConservativeGCTest mark(T *thing, JSTracer *trc);
     void markDelayedChildren(JSTracer *trc);
     inline bool inFreeList(void *thing) const;
-    inline T *getAlignedThing(void *thing);
+    inline T *getAlignedThing(const void *thing);
 #ifdef DEBUG
     inline bool assureThingIsAligned(void *thing);
 #endif
@@ -428,7 +428,7 @@ Arena<T>::bitmap() const
 
 template <typename T>
 inline T *
-Arena<T>::getAlignedThing(void *thing)
+Arena<T>::getAlignedThing(const void *thing)
 {
     jsuword start = reinterpret_cast<jsuword>(&t.things[0]);
     jsuword offset = reinterpret_cast<jsuword>(thing) - start;
@@ -533,7 +533,7 @@ GetFinalizableTraceKind(size_t thingKind)
 }
 
 inline uint32
-GetGCThingTraceKind(void *thing);
+GetGCThingTraceKind(const void *thing);
 
 static inline JSRuntime *
 GetGCThingRuntime(void *thing)
@@ -773,7 +773,7 @@ extern void
 js_UnlockGCThingRT(JSRuntime *rt, void *thing);
 
 extern JS_FRIEND_API(bool)
-IsAboutToBeFinalized(JSContext *cx, void *thing);
+IsAboutToBeFinalized(JSContext *cx, const void *thing);
 
 extern JS_FRIEND_API(bool)
 js_GCThingIsMarked(void *thing, uintN color);
@@ -1013,7 +1013,7 @@ struct GCMarker : public JSTracer {
         color = newColor;
     }
 
-    void delayMarkingChildren(void *thing);
+    void delayMarkingChildren(const void *thing);
 
     JS_FRIEND_API(void) markDelayedChildren();
 };
diff --git a/js/src/jsgcinlines.h b/js/src/jsgcinlines.h
index f8ec5fae473d..ef8d7e4d14c2 100644
--- a/js/src/jsgcinlines.h
+++ b/js/src/jsgcinlines.h
@@ -57,7 +57,7 @@
 #endif
 
 inline bool
-JSAtom::isUnitString(void *ptr)
+JSAtom::isUnitString(const void *ptr)
 {
     jsuword delta = reinterpret_cast<jsuword>(ptr) -
                     reinterpret_cast<jsuword>(unitStaticTable);
@@ -70,7 +70,7 @@ JSAtom::isUnitString(void *ptr)
 }
 
 inline bool
-JSAtom::isLength2String(void *ptr)
+JSAtom::isLength2String(const void *ptr)
 {
     jsuword delta = reinterpret_cast<jsuword>(ptr) -
                     reinterpret_cast<jsuword>(length2StaticTable);
@@ -83,7 +83,7 @@ JSAtom::isLength2String(void *ptr)
 }
 
 inline bool
-JSAtom::isHundredString(void *ptr)
+JSAtom::isHundredString(const void *ptr)
 {
     jsuword delta = reinterpret_cast<jsuword>(ptr) -
                     reinterpret_cast<jsuword>(hundredStaticTable);
@@ -96,7 +96,7 @@ JSAtom::isHundredString(void *ptr)
 }
 
 inline bool
-JSAtom::isStatic(void *ptr)
+JSAtom::isStatic(const void *ptr)
 {
     return isUnitString(ptr) || isLength2String(ptr) || isHundredString(ptr);
 }
@@ -105,12 +105,12 @@ namespace js {
 namespace gc {
 
 inline uint32
-GetGCThingTraceKind(void *thing)
+GetGCThingTraceKind(const void *thing)
 {
     JS_ASSERT(thing);
     if (JSAtom::isStatic(thing))
         return JSTRACE_STRING;
-    Cell *cell = reinterpret_cast<Cell *>(thing);
+    const Cell *cell = reinterpret_cast<const Cell *>(thing);
     return GetFinalizableTraceKind(cell->arena()->header()->thingKind);
 }
 
@@ -271,7 +271,7 @@ Mark(JSTracer *trc, T *thing)
 
     if (!IS_GC_MARKING_TRACER(trc)) {
         uint32 kind = js::gc::GetGCThingTraceKind(thing);
-        trc->callback(trc, thing, kind);
+        trc->callback(trc, (void *)thing, kind);
         goto out;
     }
 
diff --git a/js/src/jsstr.h b/js/src/jsstr.h
index 346da6413030..a86ea52fca61 100644
--- a/js/src/jsstr.h
+++ b/js/src/jsstr.h
@@ -590,9 +590,9 @@ class JSAtom : public JSFixedString
 
   private:
     /* Defined in jsgcinlines.h */
-    static inline bool isUnitString(void *ptr);
-    static inline bool isLength2String(void *ptr);
-    static inline bool isHundredString(void *ptr);
+    static inline bool isUnitString(const void *ptr);
+    static inline bool isLength2String(const void *ptr);
+    static inline bool isHundredString(const void *ptr);
 
     typedef uint8 SmallChar;
     static const SmallChar INVALID_SMALL_CHAR = -1;
@@ -614,7 +614,7 @@ class JSAtom : public JSFixedString
      * While this query can be used for any pointer to GC thing, given a
      * JSString 'str', it is more efficient to use 'str->isStaticAtom()'.
      */
-    static inline bool isStatic(void *ptr);
+    static inline bool isStatic(const void *ptr);
 
     static inline bool hasIntStatic(int32 i);
     static inline JSStaticAtom &intStatic(jsint i);