diff --git a/js/src/proxy/CrossCompartmentWrapper.cpp b/js/src/proxy/CrossCompartmentWrapper.cpp
index 94d4cdcd2673..035ae0f467a9 100644
--- a/js/src/proxy/CrossCompartmentWrapper.cpp
+++ b/js/src/proxy/CrossCompartmentWrapper.cpp
@@ -678,13 +678,12 @@ js::RemapAllWrappersForObject(JSContext* cx, JSObject* oldTargetArg,
     RootedObject newTarget(cx, newTargetArg);
 
     AutoWrapperVector toTransplant(cx);
-    if (!toTransplant.reserve(cx->runtime()->numCompartments))
-        return false;
 
     for (CompartmentsIter c(cx->runtime()); !c.done(); c.next()) {
         if (WrapperMap::Ptr wp = c->lookupWrapper(origv)) {
             // We found a wrapper. Remember and root it.
-            toTransplant.infallibleAppend(WrapperValue(wp));
+            if (!toTransplant.append(WrapperValue(wp)))
+                return false;
         }
     }
 
diff --git a/js/src/vm/JSCompartment.cpp b/js/src/vm/JSCompartment.cpp
index 53cb42cb48e0..2cb05c8765a2 100644
--- a/js/src/vm/JSCompartment.cpp
+++ b/js/src/vm/JSCompartment.cpp
@@ -44,9 +44,7 @@ using mozilla::PodArrayZero;
 JSCompartment::JSCompartment(Zone* zone)
   : zone_(zone),
     runtime_(zone->runtimeFromAnyThread())
-{
-    runtime_->numCompartments++;
-}
+{}
 
 ObjectRealm::ObjectRealm(JS::Zone* zone)
   : innerViews(zone)
@@ -69,6 +67,8 @@ Realm::Realm(JS::Zone* zone, const JS::RealmOptions& options)
 {
     MOZ_ASSERT_IF(creationOptions_.mergeable(),
                   creationOptions_.invisibleToDebugger());
+
+    runtime_->numRealms++;
 }
 
 Realm::~Realm()
@@ -84,11 +84,9 @@ Realm::~Realm()
     if (!runtime_->gc.shutdownCollectedEverything())
         objectGroups_.unboxedLayouts.clear();
 #endif
-}
 
-JSCompartment::~JSCompartment()
-{
-    runtime_->numCompartments--;
+    MOZ_ASSERT(runtime_->numRealms > 0);
+    runtime_->numRealms--;
 }
 
 bool
diff --git a/js/src/vm/JSCompartment.h b/js/src/vm/JSCompartment.h
index 0b5e36c7b385..857ebc91f7d9 100644
--- a/js/src/vm/JSCompartment.h
+++ b/js/src/vm/JSCompartment.h
@@ -618,7 +618,6 @@ struct JSCompartment
 
   protected:
     explicit JSCompartment(JS::Zone* zone);
-    ~JSCompartment();
 
     MOZ_MUST_USE bool init(JSContext* cx);
 
diff --git a/js/src/vm/MemoryMetrics.cpp b/js/src/vm/MemoryMetrics.cpp
index a314e12e817b..56c5fde2bfee 100644
--- a/js/src/vm/MemoryMetrics.cpp
+++ b/js/src/vm/MemoryMetrics.cpp
@@ -762,7 +762,7 @@ CollectRuntimeStatsHelper(JSContext* cx, RuntimeStats* rtStats, ObjectPrivateVis
                           bool anonymize, IterateCellCallback statsCellCallback)
 {
     JSRuntime* rt = cx->runtime();
-    if (!rtStats->realmStatsVector.reserve(rt->numCompartments))
+    if (!rtStats->realmStatsVector.reserve(rt->numRealms))
         return false;
 
     size_t totalZones = rt->gc.zones().length() + 1; // + 1 for the atoms zone.
diff --git a/js/src/vm/Runtime.cpp b/js/src/vm/Runtime.cpp
index 430ad91088ad..ae8beb139bff 100644
--- a/js/src/vm/Runtime.cpp
+++ b/js/src/vm/Runtime.cpp
@@ -133,7 +133,7 @@ JSRuntime::JSRuntime(JSRuntime* parentRuntime)
     activeThreadHasScriptDataAccess(false),
 #endif
     numActiveHelperThreadZones(0),
-    numCompartments(0),
+    numRealms(0),
     localeCallbacks(nullptr),
     defaultLocale(nullptr),
     profilingScripts(false),
diff --git a/js/src/vm/Runtime.h b/js/src/vm/Runtime.h
index 59ecc7182353..fec75795bc93 100644
--- a/js/src/vm/Runtime.h
+++ b/js/src/vm/Runtime.h
@@ -511,10 +511,10 @@ struct JSRuntime : public js::MallocProvider<JSRuntime>
     }
 #endif
 
-    // How many compartments there are across all zones. This number includes
-    // off thread context compartments, so it isn't necessarily equal to the
-    // number of compartments visited by CompartmentsIter.
-    js::MainThreadData<size_t> numCompartments;
+    // How many realms there are across all zones. This number includes
+    // off-thread context realms, so it isn't necessarily equal to the
+    // number of realms visited by RealmsIter.
+    js::MainThreadData<size_t> numRealms;
 
     /* Locale-specific callbacks for string conversion. */
     js::MainThreadData<const JSLocaleCallbacks*> localeCallbacks;