diff --git a/impl/src/main/java/com/sun/faces/facelets/tag/jsf/IterationIdManager.java b/impl/src/main/java/com/sun/faces/facelets/tag/jsf/IterationIdManager.java
index 601cb07be4..fd22c2578a 100644
--- a/impl/src/main/java/com/sun/faces/facelets/tag/jsf/IterationIdManager.java
+++ b/impl/src/main/java/com/sun/faces/facelets/tag/jsf/IterationIdManager.java
@@ -82,8 +82,13 @@ static boolean isIterating(FaceletContext context){
     private static Deque<Set<String>> _getStackOfTrackedIds(FaceletContext ctx) {
         Deque<Set<String>> stack = (Deque<Set<String>>)ctx.getAttribute(_STACK_OF_TRACKED_IDS);
         if (stack == null) {
-            stack = new LinkedList<>();
-            ctx.setAttribute(_STACK_OF_TRACKED_IDS, stack);
+            synchronized(IterationIdManager.class) {
+                stack = (Deque<Set<String>>)ctx.getAttribute(_STACK_OF_TRACKED_IDS);
+                if(stack == null) {
+                   stack = new LinkedList<>();
+                   ctx.setAttribute(_STACK_OF_TRACKED_IDS, stack);
+                }
+            }
         }
         return stack;
     }