diff --git a/js/src/jit-test/lib/prolog.js b/js/src/jit-test/lib/prolog.js
index 54ddabde597..eccb7291c21 100644
--- a/js/src/jit-test/lib/prolog.js
+++ b/js/src/jit-test/lib/prolog.js
@@ -32,5 +32,9 @@ if (!("verifypostbarriers" in this)) {
   verifypostbarriers = function() { }
 }
 
+if (!("gcPreserveCode" in this)) {
+  gcPreserveCode = function() { }
+}
+
 if ("options" in this)
     options("allow_xml");
diff --git a/js/src/jsgc.cpp b/js/src/jsgc.cpp
index 5a9c37b5194..6a9af5bc9fe 100644
--- a/js/src/jsgc.cpp
+++ b/js/src/jsgc.cpp
@@ -4079,7 +4079,7 @@ ResetIncrementalGC(JSRuntime *rt, const char *reason)
         AutoCopyFreeListToArenas copy(rt);
         for (GCCompartmentsIter c(rt); !c.done(); c.next()) {
             if (c->isGCMarking()) {
-                c->setNeedsBarrier(false, JSCompartment::DontUpdateIon);
+                c->setNeedsBarrier(false, JSCompartment::UpdateIon);
                 c->setGCState(JSCompartment::NoGC);
                 wasMarking = true;
             }
@@ -4154,12 +4154,12 @@ AutoGCSlice::AutoGCSlice(JSRuntime *rt)
 
 AutoGCSlice::~AutoGCSlice()
 {
-    for (GCCompartmentsIter c(runtime); !c.done(); c.next()) {
+    /* We can't use GCCompartmentsIter if this is the end of the last slice. */
+    for (CompartmentsIter c(runtime); !c.done(); c.next()) {
         if (c->isGCMarking()) {
             c->setNeedsBarrier(true, JSCompartment::UpdateIon);
             c->arenas.prepareForIncrementalGC(runtime);
         } else {
-            JS_ASSERT(c->isGCSweeping());
             c->setNeedsBarrier(false, JSCompartment::UpdateIon);
         }
     }