diff --git a/runtime/ztests/expr/is-null.yaml b/runtime/ztests/expr/is-null.yaml
index eb80c0dd90..a6509b9011 100644
--- a/runtime/ztests/expr/is-null.yaml
+++ b/runtime/ztests/expr/is-null.yaml
@@ -6,7 +6,7 @@ input: |
   fusion("foo"::(string|null),<string>)
   null
   null::(int64|null)
-  fusion(null::(int64|null),<string>)
+  fusion(null::(int64|null),<null>)
   error("missing")
   error("foo")