diff --git a/src/structure/parallel_structure.ts b/src/structure/parallel_structure.ts
index ce283b19bc873f693a2d4a1d4c2a8eb21f285c15..255051775431ddfd5353dee194a8ee5c125c76ef 100644
--- a/src/structure/parallel_structure.ts
+++ b/src/structure/parallel_structure.ts
@@ -116,6 +116,9 @@ export class ParallelStructure extends Nub {
         for (let i = 0; i < this._children.length; i++) {
             if (i !== iExcept) {
                 const res: Result = this._children[i].Calc("Q");
+                if (!res.ok) {
+                    return res;
+                }
                 qTot += res.vCalc;
                 // merge logs
                 calcRes.resultElement.log.addLog(res.log);