diff --git a/src/heap/heap.cc b/src/heap/heap.cc
index 82589c7fd9..38a31bc210 100644
--- a/src/heap/heap.cc
+++ b/src/heap/heap.cc
@@ -874,7 +874,8 @@ bool Heap::CollectGarbage(GarbageCollector collector, const char* gc_reason,
   // Start incremental marking for the next cycle. The heap snapshot
   // generator needs incremental marking to stay off after it aborted.
   if (!mark_compact_collector()->abort_incremental_marking() &&
-      WorthActivatingIncrementalMarking()) {
+      incremental_marking()->IsStopped() &&
+      incremental_marking()->ShouldActivateEvenWithoutIdleNotification()) {
     incremental_marking()->Start();
   }
 
@@ -4545,12 +4546,6 @@ bool Heap::TryFinalizeIdleIncrementalMarking(
 }
 
 
-bool Heap::WorthActivatingIncrementalMarking() {
-  return incremental_marking()->IsStopped() &&
-         incremental_marking()->ShouldActivate();
-}
-
-
 static double MonotonicallyIncreasingTimeInMs() {
   return V8::GetCurrentPlatform()->MonotonicallyIncreasingTime() *
          static_cast<double>(base::Time::kMillisecondsPerSecond);
@@ -4588,8 +4583,8 @@ bool Heap::IdleNotification(double deadline_in_seconds) {
   }
 
   heap_state.can_start_incremental_marking =
-      incremental_marking()->WorthActivating() &&
-      NextGCIsLikelyToBeFull(limit) && FLAG_incremental_marking &&
+      incremental_marking()->CanBeActivated() &&
+      HeapIsFullEnoughToStartIncrementalMarking(limit) &&
       !mark_compact_collector()->sweeping_in_progress();
   heap_state.sweeping_in_progress =
       mark_compact_collector()->sweeping_in_progress();
diff --git a/src/heap/heap.h b/src/heap/heap.h
index 5dfae06c3a..4bcfcbb80a 100644
--- a/src/heap/heap.h
+++ b/src/heap/heap.h
@@ -1241,9 +1241,7 @@ class Heap {
     survived_since_last_expansion_ += survived;
   }
 
-  inline bool NextGCIsLikelyToBeFull(intptr_t limit) {
-    if (FLAG_gc_global) return true;
-
+  inline bool HeapIsFullEnoughToStartIncrementalMarking(intptr_t limit) {
     if (FLAG_stress_compaction && (gc_count_ & 1) != 0) return true;
 
     intptr_t adjusted_allocation_limit = limit - new_space_.Capacity();
@@ -2083,8 +2081,6 @@ class Heap {
       double idle_time_in_ms, size_t size_of_objects,
       size_t mark_compact_speed_in_bytes_per_ms);
 
-  bool WorthActivatingIncrementalMarking();
-
   void ClearObjectStats(bool clear_last_time_stats = false);
 
   inline void UpdateAllocationsHash(HeapObject* object);
diff --git a/src/heap/incremental-marking.cc b/src/heap/incremental-marking.cc
index ef2e113785..17c609c3f6 100644
--- a/src/heap/incremental-marking.cc
+++ b/src/heap/incremental-marking.cc
@@ -386,9 +386,9 @@ void IncrementalMarking::ActivateIncrementalWriteBarrier() {
 }
 
 
-bool IncrementalMarking::ShouldActivate() {
-  return WorthActivating() &&
-         heap_->NextGCIsLikelyToBeFull(
+bool IncrementalMarking::ShouldActivateEvenWithoutIdleNotification() {
+  return CanBeActivated() &&
+         heap_->HeapIsFullEnoughToStartIncrementalMarking(
              heap_->old_generation_allocation_limit());
 }
 
@@ -396,7 +396,7 @@ bool IncrementalMarking::ShouldActivate() {
 bool IncrementalMarking::WasActivated() { return was_activated_; }
 
 
-bool IncrementalMarking::WorthActivating() {
+bool IncrementalMarking::CanBeActivated() {
 #ifndef DEBUG
   static const intptr_t kActivationThreshold = 8 * MB;
 #else
@@ -407,6 +407,7 @@ bool IncrementalMarking::WorthActivating() {
   // Only start incremental marking in a safe state: 1) when incremental
   // marking is turned on, 2) when we are currently not in a GC, and
   // 3) when we are currently not serializing or deserializing the heap.
+  // Don't switch on for very small heaps.
   return FLAG_incremental_marking && FLAG_incremental_marking_steps &&
          heap_->gc_state() == Heap::NOT_IN_GC &&
          heap_->deserialization_complete() &&
@@ -814,7 +815,7 @@ void IncrementalMarking::Epilogue() {
 
 
 void IncrementalMarking::OldSpaceStep(intptr_t allocated) {
-  if (IsStopped() && ShouldActivate()) {
+  if (IsStopped() && ShouldActivateEvenWithoutIdleNotification()) {
     Start();
   } else {
     Step(allocated * kOldSpaceAllocationMarkingFactor, GC_VIA_STACK_GUARD);
diff --git a/src/heap/incremental-marking.h b/src/heap/incremental-marking.h
index 03642c1020..51633233fe 100644
--- a/src/heap/incremental-marking.h
+++ b/src/heap/incremental-marking.h
@@ -64,9 +64,9 @@ class IncrementalMarking {
 
   GCRequestType request_type() const { return request_type_; }
 
-  bool WorthActivating();
+  bool CanBeActivated();
 
-  bool ShouldActivate();
+  bool ShouldActivateEvenWithoutIdleNotification();
 
   bool WasActivated();