diff --git a/src/diff/index.js b/src/diff/index.js
index 9f11a182d1..3e4b17bd62 100644
--- a/src/diff/index.js
+++ b/src/diff/index.js
@@ -563,6 +563,7 @@ export function applyRef(ref, value, vnode) {
 		if (typeof ref == 'function') {
 			let hasRefUnmount = typeof ref._unmount == 'function';
 			if (hasRefUnmount) {
+				// @ts-ignore TS doesn't like moving narrowing checks into variables
 				ref._unmount();
 			}