diff --git a/tests/lean/run/issue7408.lean b/tests/lean/run/issue7408.lean
index 45e7c32e2a..d00e4f6bff 100644
--- a/tests/lean/run/issue7408.lean
+++ b/tests/lean/run/issue7408.lean
@@ -1,7 +1,8 @@
 def computeFuel (mass : Nat) : Nat :=
   let rec go acc cur :=
     let n := cur / 3 - 2
-    if n = 0 then acc + cur else go (acc + cur) n
+    -- TODO: investigate why we need `_ :`
+    if _ : n = 0 then acc + cur else go (acc + cur) n
   termination_by cur
   go 0 mass - mass