diff --git a/js/src/jsgc.cpp b/js/src/jsgc.cpp
index 0fcd96193f2..6a99ce4ec09 100644
--- a/js/src/jsgc.cpp
+++ b/js/src/jsgc.cpp
@@ -5520,10 +5520,6 @@ GCRuntime::compactPhase(JS::gcreason::Reason reason)
     }
 #endif
 
-    // Ensure execess chunks are returns to the system and free arenas
-    // decommitted.
-    shrinkBuffers();
-
 #ifdef DEBUG
     CheckHashTablesAfterMovingGC(rt);
     for (GCZonesIter zone(rt); !zone.done(); zone.next()) {
@@ -5569,6 +5565,10 @@ GCRuntime::finishCollection(JS::gcreason::Reason reason)
         MOZ_ASSERT(!zone->wasGCStarted());
     }
 
+    // Ensure execess chunks are returned to the system and free arenas
+    // decommitted.
+    shrinkBuffers();
+
     lastGCTime = currentTime;
 
     // If this is an OOM GC reason, wait on the background sweeping thread