diff --git a/js/src/gc/GCInternals.h b/js/src/gc/GCInternals.h
index 9b34a3207b14..723636f41925 100644
--- a/js/src/gc/GCInternals.h
+++ b/js/src/gc/GCInternals.h
@@ -8,6 +8,7 @@
 #define gc_GCInternals_h
 
 #include "mozilla/ArrayUtils.h"
+#include "mozilla/Maybe.h"
 #include "mozilla/PodOperations.h"
 
 #include "jscntxt.h"
@@ -19,10 +20,7 @@
 namespace js {
 namespace gc {
 
-struct MOZ_RAII AutoFinishGC
-{
-    explicit AutoFinishGC(JSRuntime* rt);
-};
+void FinishGC(JSRuntime* rt);
 
 /*
  * This class should be used by any code that needs to exclusive access to the
@@ -48,8 +46,7 @@ class MOZ_RAII AutoTraceSession
 
 struct MOZ_RAII AutoPrepareForTracing
 {
-    AutoFinishGC finish;
-    AutoTraceSession session;
+    mozilla::Maybe<AutoTraceSession> session;
 
     AutoPrepareForTracing(JSRuntime* rt, ZoneSelector selector);
 };
diff --git a/js/src/jsapi-tests/testGCAllocator.cpp b/js/src/jsapi-tests/testGCAllocator.cpp
index f9c8058ec20a..025ff307d5df 100644
--- a/js/src/jsapi-tests/testGCAllocator.cpp
+++ b/js/src/jsapi-tests/testGCAllocator.cpp
@@ -48,7 +48,7 @@ BEGIN_TEST(testGCAllocator)
 #endif
 
     /* Finish any ongoing background free activity. */
-    js::gc::AutoFinishGC finishGC(rt);
+    js::gc::FinishGC(rt);
 
     bool growUp;
     CHECK(addressesGrowUp(&growUp));
diff --git a/js/src/jsapi-tests/testGCUniqueId.cpp b/js/src/jsapi-tests/testGCUniqueId.cpp
index 40feadf1018f..09f2fac8eb34 100644
--- a/js/src/jsapi-tests/testGCUniqueId.cpp
+++ b/js/src/jsapi-tests/testGCUniqueId.cpp
@@ -18,7 +18,7 @@ MinimizeHeap(JSRuntime* rt)
     // sweeping that the first GC started to finish.
     JS_GC(rt);
     JS_GC(rt);
-    js::gc::AutoFinishGC finish(rt);
+    js::gc::FinishGC(rt);
 }
 
 BEGIN_TEST(testGCUID)
diff --git a/js/src/jsgc.cpp b/js/src/jsgc.cpp
index 57103a041ed7..8ed28268689b 100644
--- a/js/src/jsgc.cpp
+++ b/js/src/jsgc.cpp
@@ -2007,7 +2007,7 @@ AutoDisableCompactingGC::AutoDisableCompactingGC(JSRuntime* rt)
 {
     gc.disableCompactingGC();
     if (gc.isIncrementalGCInProgress() && gc.isCompactingGc())
-        AutoFinishGC finishGC(rt);
+        FinishGC(rt);
 }
 
 AutoDisableCompactingGC::~AutoDisableCompactingGC()
@@ -6726,21 +6726,20 @@ GCRuntime::gcIfRequested(JSContext* cx /* = nullptr */)
     return false;
 }
 
-AutoFinishGC::AutoFinishGC(JSRuntime* rt)
+void js::gc::FinishGC(JSRuntime* rt)
 {
     if (JS::IsIncrementalGCInProgress(rt)) {
         JS::PrepareForIncrementalGC(rt);
         JS::FinishIncrementalGC(rt, JS::gcreason::API);
     }
 
-    rt->gc.waitBackgroundSweepEnd();
     rt->gc.nursery.waitBackgroundFreeEnd();
 }
 
 AutoPrepareForTracing::AutoPrepareForTracing(JSRuntime* rt, ZoneSelector selector)
-  : finish(rt),
-    session(rt)
 {
+    js::gc::FinishGC(rt);
+    session.emplace(rt);
 }
 
 JSCompartment*
diff --git a/js/src/jsgc.h b/js/src/jsgc.h
index 4845665d24cb..c9c5b964f2a8 100644
--- a/js/src/jsgc.h
+++ b/js/src/jsgc.h
@@ -789,12 +789,6 @@ const size_t MAX_EMPTY_CHUNK_AGE = 4;
 
 } /* namespace gc */
 
-extern bool
-InitGC(JSRuntime* rt, uint32_t maxbytes);
-
-extern void
-FinishGC(JSRuntime* rt);
-
 class InterpreterFrame;
 
 extern void
diff --git a/js/src/shell/js.cpp b/js/src/shell/js.cpp
index 5d3cd1cafbaa..ecb61d45bbb4 100644
--- a/js/src/shell/js.cpp
+++ b/js/src/shell/js.cpp
@@ -3812,7 +3812,7 @@ runOffThreadScript(JSContext* cx, unsigned argc, Value* vp)
 
     JSRuntime* rt = cx->runtime();
     if (OffThreadParsingMustWaitForGC(rt))
-        gc::AutoFinishGC finishgc(rt);
+        gc::FinishGC(rt);
 
     void* token = offThreadState.waitUntilDone(cx, ScriptKind::Script);
     if (!token) {
@@ -3914,7 +3914,7 @@ FinishOffThreadModule(JSContext* cx, unsigned argc, Value* vp)
 
     JSRuntime* rt = cx->runtime();
     if (OffThreadParsingMustWaitForGC(rt))
-        gc::AutoFinishGC finishgc(rt);
+        gc::FinishGC(rt);
 
     void* token = offThreadState.waitUntilDone(cx, ScriptKind::Module);
     if (!token) {
diff --git a/js/src/vm/HelperThreads.cpp b/js/src/vm/HelperThreads.cpp
index 0a297207d905..de4fbeb04f20 100644
--- a/js/src/vm/HelperThreads.cpp
+++ b/js/src/vm/HelperThreads.cpp
@@ -1240,7 +1240,7 @@ GlobalHelperThreadState::mergeParseTaskCompartment(JSRuntime* rt, ParseTask* par
     // finished merging the contents of the parse task's compartment into the
     // destination compartment.  Finish any ongoing incremental GC first and
     // assert that no allocation can occur.
-    gc::AutoFinishGC finishGC(rt);
+    gc::FinishGC(rt);
     JS::AutoAssertNoAlloc noAlloc(rt);
 
     LeaveParseTaskZone(rt, parseTask);