diff --git a/rsconcept/frontend/src/pages/OssPage/OssTabs.tsx b/rsconcept/frontend/src/pages/OssPage/OssTabs.tsx
index 5aa06d42..d224666d 100644
--- a/rsconcept/frontend/src/pages/OssPage/OssTabs.tsx
+++ b/rsconcept/frontend/src/pages/OssPage/OssTabs.tsx
@@ -33,7 +33,7 @@ export enum OssTabID {
 function OssTabs() {
   const router = useConceptNavigation();
   const query = useQueryStrings();
-  const activeTab = (Number(query.get('tab')) ?? OssTabID.GRAPH) as OssTabID;
+  const activeTab = query.get('tab') ? (Number(query.get('tab')) as OssTabID) : OssTabID.GRAPH;
 
   const { calculateHeight } = useConceptOptions();
   const { schema, loading, errorLoading } = useOSS();
diff --git a/rsconcept/frontend/src/pages/RSFormPage/RSTabs.tsx b/rsconcept/frontend/src/pages/RSFormPage/RSTabs.tsx
index 76e6768f..46072b31 100644
--- a/rsconcept/frontend/src/pages/RSFormPage/RSTabs.tsx
+++ b/rsconcept/frontend/src/pages/RSFormPage/RSTabs.tsx
@@ -40,7 +40,7 @@ export enum RSTabID {
 function RSTabs() {
   const router = useConceptNavigation();
   const query = useQueryStrings();
-  const activeTab = (Number(query.get('tab')) ?? RSTabID.CARD) as RSTabID;
+  const activeTab = query.get('tab') ? (Number(query.get('tab')) as RSTabID) : RSTabID.CARD;
   const version = query.get('v') ? Number(query.get('v')) : undefined;
   const cstQuery = query.get('active');