diff --git a/ci/default.nix b/ci/default.nix
index 540a0faea0ab..2be2a17c6f2c 100644
--- a/ci/default.nix
+++ b/ci/default.nix
@@ -184,9 +184,10 @@ rec {
     nix = pkgs.nixVersions.latest;
   };
   parse = pkgs.lib.recurseIntoAttrs {
-    latest = pkgs.callPackage ./parse.nix { nix = pkgs.nixVersions.latest; };
-    lix = pkgs.callPackage ./parse.nix { nix = pkgs.lix; };
+    nix_latest = pkgs.callPackage ./parse.nix { nix = pkgs.nixVersions.latest; };
     nix_2_28 = pkgs.callPackage ./parse.nix { nix = pkgs.nixVersions.nix_2_28; };
+    lix = pkgs.callPackage ./parse.nix { nix = pkgs.lix; };
+    lix_latest = pkgs.callPackage ./parse.nix { nix = pkgs.lixPackageSets.latest.lix; };
   };
   shell = import ../shell.nix { inherit nixpkgs system; };
   tarball = import ../pkgs/top-level/make-tarball.nix {
diff --git a/ci/parse.nix b/ci/parse.nix
index 14fd1e719547..8c9a84b446b1 100644
--- a/ci/parse.nix
+++ b/ci/parse.nix
@@ -28,7 +28,14 @@ runCommand "nix-parse-${nix.name}"
     # the other CI jobs will report in more detail. This job is about checking parsing
     # across different implementations / versions, not about providing the best DX.
     # Returning all parse errors requires significantly more resources.
-    find . -type f -iname '*.nix' | xargs -P $(nproc) nix-instantiate --parse >/dev/null
+
+    find . -type f -iname '*.nix' | xargs -P $(nproc) nix-instantiate --parse 2>&1 >/dev/null | {
+      # Also fail on (deprecation) warnings printed to stderr.
+      if grep "warning"; then
+        echo "Failing due to warnings in stderr" >&2
+        exit 1
+      fi
+    }
 
     touch $out
   ''