diff --git a/frontend/src/components/unification/Unification/UnificationRightPane.vue b/frontend/src/components/unification/Unification/UnificationRightPane.vue
index 5247642dd82167ba2fb54349bb9d0122f9d42e45..7f306864e8292bc3748a52936c679f7ec69dc309 100644
--- a/frontend/src/components/unification/Unification/UnificationRightPane.vue
+++ b/frontend/src/components/unification/Unification/UnificationRightPane.vue
@@ -18,7 +18,7 @@ export default {
         key: this.lexicalUnitId,
         entryIdLocal: this.entryId,
         unifiedFrameId: this.initialUnifiedFrameId,
-        previewedUnifiedFrameId: null
+        previewedUnifiedFrameId: -1
       };
     },
     goToDisplay() {
diff --git a/frontend/src/components/unification/hierarchy/HierarchyRightPane.vue b/frontend/src/components/unification/hierarchy/HierarchyRightPane.vue
index 913bbf73ff32d8e620d7e127760f826e20c8b768..e21bfd40ea014efeae452fcd0f56a36d920c1a80 100644
--- a/frontend/src/components/unification/hierarchy/HierarchyRightPane.vue
+++ b/frontend/src/components/unification/hierarchy/HierarchyRightPane.vue
@@ -18,7 +18,7 @@ export default {
         key: this.lexicalUnitId,
         entryIdLocal: this.entryId,
         unifiedFrameId: this.initialUnifiedFrameId,
-        previewedUnifiedFrameId: null
+        previewedUnifiedFrameId: -1
       };
     },
     goToDisplay() {