diff --git a/src/hotspot/share/gc/shenandoah/heuristics/shenandoahAdaptiveHeuristics.cpp b/src/hotspot/share/gc/shenandoah/heuristics/shenandoahAdaptiveHeuristics.cpp
index 7d8afea767a..720d2553728 100644
--- a/src/hotspot/share/gc/shenandoah/heuristics/shenandoahAdaptiveHeuristics.cpp
+++ b/src/hotspot/share/gc/shenandoah/heuristics/shenandoahAdaptiveHeuristics.cpp
@@ -182,7 +182,7 @@ void ShenandoahAdaptiveHeuristics::resume_idle_span() {
 // There is no headroom during evacuation and update refs.  This information is not used to trigger the next GC.
 // In future implementations, this information may feed into worker surge calculations.
 void ShenandoahAdaptiveHeuristics::start_evac_span() {
-  size_t mutator_available = _free_set->capacity() - _free_set->used();
+  size_t mutator_available = _free_set->available_holding_lock();
   _trigger_threshold = mutator_available;
 }
 
diff --git a/src/hotspot/share/gc/shenandoah/shenandoahFreeSet.hpp b/src/hotspot/share/gc/shenandoah/shenandoahFreeSet.hpp
index a016a598794..f7d64696763 100644
--- a/src/hotspot/share/gc/shenandoah/shenandoahFreeSet.hpp
+++ b/src/hotspot/share/gc/shenandoah/shenandoahFreeSet.hpp
@@ -845,11 +845,14 @@ public:
     ShenandoahRebuildLocker locker(rebuild_lock());
     return _partitions.used_by(ShenandoahFreeSetPartitionId::Mutator);
   }
+  inline size_t reserved()  const { return _partitions.capacity_of(ShenandoahFreeSetPartitionId::Collector);           }
   inline size_t available() {
     shenandoah_assert_not_heaplocked();
     ShenandoahRebuildLocker locker(rebuild_lock());
     return _partitions.available_in_locked_for_rebuild(ShenandoahFreeSetPartitionId::Mutator);
   }
+  inline size_t available_holding_lock() const
+                                  { return _partitions.available_in(ShenandoahFreeSetPartitionId::Mutator); }
 
   inline size_t total_humongous_waste() const      { return _total_humongous_waste; }
   inline size_t humongous_waste_in_mutator() const { return _partitions.humongous_waste(ShenandoahFreeSetPartitionId::Mutator); }