diff --git a/webapp/src/components/App/Studies/StudyTree/utils.ts b/webapp/src/components/App/Studies/StudyTree/utils.ts
index bb758cdb89..20958866dd 100644
--- a/webapp/src/components/App/Studies/StudyTree/utils.ts
+++ b/webapp/src/components/App/Studies/StudyTree/utils.ts
@@ -308,10 +308,10 @@ export function mergeDeepRightStudyTree(left: StudyTreeNode, right: StudyTreeNod
  * @returns list of tuples where the first element is from the left list and the second element is from the right list.
  */
 export function innerJoin(
-  left: Array<StudyTreeNode>,
-  right: Array<StudyTreeNode>,
+  left: StudyTreeNode[],
+  right: StudyTreeNode[],
 ): Array<[StudyTreeNode, StudyTreeNode]> {
-  return left.reduce<[StudyTreeNode, StudyTreeNode][]>((acc, leftNode) => {
+  return left.reduce<Array<[StudyTreeNode, StudyTreeNode]>>((acc, leftNode) => {
     const matchedRightNode = right.find((rightNode) => rightNode.name === leftNode.name);
     if (matchedRightNode) {
       acc.push([{ ...leftNode }, { ...matchedRightNode }]);