diff --git a/src/Lean/Server/References.lean b/src/Lean/Server/References.lean
index 9029a16cf8..20d542214b 100644
--- a/src/Lean/Server/References.lean
+++ b/src/Lean/Server/References.lean
@@ -193,7 +193,7 @@ where
           insertIdMap id baseId
 
     -- apply `FVarAliasInfo`
-    trees.forM (·.visitM' (postNode := fun _ info cs => do
+    trees.forM (·.visitM' (postNode := fun _ info _ => do
       if let .ofFVarAliasInfo ai := info then
         insertIdMap ai.id ai.baseId))