diff --git a/helix-core/src/main/java/org/apache/helix/controller/dataproviders/WorkflowControllerDataProvider.java b/helix-core/src/main/java/org/apache/helix/controller/dataproviders/WorkflowControllerDataProvider.java
index 3a71e777bf..52e27987fc 100644
--- a/helix-core/src/main/java/org/apache/helix/controller/dataproviders/WorkflowControllerDataProvider.java
+++ b/helix-core/src/main/java/org/apache/helix/controller/dataproviders/WorkflowControllerDataProvider.java
@@ -189,7 +189,7 @@ private void fillActiveTaskCount(Map<String, Integer> additionPartitionMap,
       Map<String, Integer> partitionMap) {
     for (String participant : additionPartitionMap.keySet()) {
       partitionMap.put(participant,
-          partitionMap.get(participant) + additionPartitionMap.get(participant));
+          partitionMap.getOrDefault(participant, 0) + additionPartitionMap.getOrDefault(participant, 0));
     }
   }