diff --git a/squirrel-foundation/src/main/java/org/squirrelframework/foundation/fsm/impl/StateMachineDataImpl.java b/squirrel-foundation/src/main/java/org/squirrelframework/foundation/fsm/impl/StateMachineDataImpl.java
index 9e5e0e40..be9c1eda 100644
--- a/squirrel-foundation/src/main/java/org/squirrelframework/foundation/fsm/impl/StateMachineDataImpl.java
+++ b/squirrel-foundation/src/main/java/org/squirrelframework/foundation/fsm/impl/StateMachineDataImpl.java
@@ -171,7 +171,8 @@ public void lastActiveChildStateFor(S parentStateId, S childStateId) {
     @Override
     public void subStateFor(S parentStateId, S subStateId) {
         if (rawStateFrom(parentStateId) != null
-                && rawStateFrom(parentStateId).isParallelState()) {
+                && rawStateFrom(parentStateId).isParallelState()
+                && !parallelStatesStore.containsEntry(parentStateId, subStateId)) {
             parallelStatesStore.put(parentStateId, subStateId);
         } else {
             logger.warn("Cannot set sub states on none parallel state {}.",