diff --git a/nix/lean-dev.in b/nix/lean-dev.in
index d9774e5372..be8e76b338 100644
--- a/nix/lean-dev.in
+++ b/nix/lean-dev.in
@@ -42,8 +42,8 @@ done
 [[ "$root" == / ]] && root="@srcRoot@"
 deps="$(echo -n "$input" | nix run "$root#print-lean-deps" 2> /dev/null)"
 attrPath="check-mod"
-# HACK: use stage 0 instead of 0 inside Lean's own `src/`
-[[ -d "$root/src/Lean" && "$inputFile" == "$root/src/"* ]] && attrPath="stage0check-mod"
+# HACK: use stage 0 instead of 1 inside Lean's own `src/`
+[[ -d "$root/src/Lean" && "$(realpath "$inputFile")" == "$root/src/"* ]] && attrPath="stage0check-mod"
 for dep in $deps; do
     attrPath="$attrPath.\"$dep\""
 done