diff --git a/js/src/gc/RootMarking.cpp b/js/src/gc/RootMarking.cpp
index 4e2d322ea236..fa30966817b4 100644
--- a/js/src/gc/RootMarking.cpp
+++ b/js/src/gc/RootMarking.cpp
@@ -556,8 +556,34 @@ js::gc::GCRuntime::markRuntime(JSTracer *trc,
 void
 js::gc::GCRuntime::bufferGrayRoots()
 {
-    marker.startBufferingGrayRoots();
+    // Precondition: the state has been reset to "unused" after the last GC
+    //               and the zone's buffers have been cleared.
+    MOZ_ASSERT(grayBufferState == GrayBufferState::Unused);
+    for (GCZonesIter zone(rt); !zone.done(); zone.next())
+        MOZ_ASSERT(zone->gcGrayRoots.empty());
+
+    // The state starts at "Okay" and may be toggled to "Failed" if we OOM
+    // while marking.
+    grayBufferState = GrayBufferState::Okay;
+
+    // Transform the GCMarker into an unholy CallbackTracer doppleganger.
+    MOZ_ASSERT(!IsMarkingGray(&marker));
+    MOZ_ASSERT(IsMarkingTracer(&marker));
+    MOZ_ASSERT(!marker.callback);
+    marker.callback = GCMarker::GrayCallback;
+    MOZ_ASSERT(IsMarkingGray(&marker));
+
     if (JSTraceDataOp op = grayRootTracer.op)
         (*op)(&marker, grayRootTracer.data);
-    marker.endBufferingGrayRoots();
+
+    // Restore the GCMarker to its former correctness.
+    MOZ_ASSERT(IsMarkingGray(&marker));
+    marker.callback = nullptr;
+    MOZ_ASSERT(!IsMarkingGray(&marker));
+    MOZ_ASSERT(IsMarkingTracer(&marker));
+
+    // Postcondition: the state remains at "Okay", or has been toggled to
+    //                "Failed" during marking.
+    MOZ_ASSERT(grayBufferState == GrayBufferState::Okay ||
+               grayBufferState == GrayBufferState::Failed);
 }
diff --git a/js/src/gc/Tracer.cpp b/js/src/gc/Tracer.cpp
index 02a9382b9180..938e858e782c 100644
--- a/js/src/gc/Tracer.cpp
+++ b/js/src/gc/Tracer.cpp
@@ -652,28 +652,6 @@ GCMarker::hasBufferedGrayRoots() const
     return runtime()->gc.grayBufferState == GCRuntime::GrayBufferState::Okay;
 }
 
-void
-GCMarker::startBufferingGrayRoots()
-{
-    MOZ_ASSERT(runtime()->gc.grayBufferState == GCRuntime::GrayBufferState::Unused);
-    runtime()->gc.grayBufferState = GCRuntime::GrayBufferState::Okay;
-    for (GCZonesIter zone(runtime()); !zone.done(); zone.next())
-        MOZ_ASSERT(zone->gcGrayRoots.empty());
-
-    MOZ_ASSERT(!callback);
-    callback = GrayCallback;
-    MOZ_ASSERT(IsMarkingGray(this));
-}
-
-void
-GCMarker::endBufferingGrayRoots()
-{
-    MOZ_ASSERT(IsMarkingGray(this));
-    callback = nullptr;
-    MOZ_ASSERT(runtime()->gc.grayBufferState == GCRuntime::GrayBufferState::Okay ||
-               runtime()->gc.grayBufferState == GCRuntime::GrayBufferState::Failed);
-}
-
 void
 GCMarker::resetBufferedGrayRoots()
 {
diff --git a/js/src/gc/Tracer.h b/js/src/gc/Tracer.h
index b2548ea6fb28..c2a42aa912b6 100644
--- a/js/src/gc/Tracer.h
+++ b/js/src/gc/Tracer.h
@@ -211,8 +211,6 @@ class GCMarker : public JSTracer
      * non-incremental GC.
      */
     bool hasBufferedGrayRoots() const;
-    void startBufferingGrayRoots();
-    void endBufferingGrayRoots();
     void resetBufferedGrayRoots();
 
     static void GrayCallback(JSTracer *trc, void **thing, JSGCTraceKind kind);