diff --git a/tests/e2e/terminal-reattach-mouse-mode-leak.spec.ts b/tests/e2e/terminal-reattach-mouse-mode-leak.spec.ts
index 021ad83cefb..e37f95e0372 100644
--- a/tests/e2e/terminal-reattach-mouse-mode-leak.spec.ts
+++ b/tests/e2e/terminal-reattach-mouse-mode-leak.spec.ts
@@ -154,7 +154,7 @@ test.describe('reattach mouse-mode leak', () => {
       const probe = await secondLaunch.page.evaluate(async () => {
         // An SGR mouse report is `ESC [ < params (M|m)`; the `ESC [ <` prefix is
         // unambiguous, so substring matching avoids a control-char regex.
-        const isMouseReport = (data) => data.includes('\x1b[<')
+        const isMouseReport = (data: string): boolean => data.includes('\x1b[<')
         const state = window.__store?.getState()
         const worktreeId = state?.activeWorktreeId
         const tabId =