diff --git a/python/lean_pool/quality.py b/python/lean_pool/quality.py
index edde5be01f..88ec2fc028 100644
--- a/python/lean_pool/quality.py
+++ b/python/lean_pool/quality.py
@@ -392,13 +392,24 @@ def _check_axioms(root: Path) -> list[_QualityError]:
         temp_file.flush()
 
     try:
-        process = subprocess.run(
-            ["lake", "env", "lean", str(temp_path)],
-            cwd=root,
-            check=False,
-            capture_output=True,
-            text=True,
-        )
+        try:
+            process = subprocess.run(
+                ["lake", "env", "lean", str(temp_path)],
+                cwd=root,
+                check=False,
+                capture_output=True,
+                text=True,
+            )
+        except FileNotFoundError:
+            # `lake` not on PATH; surface a single advisory error rather
+            # than crashing the whole quality run.
+            return [
+                _QualityError(
+                    root / "LeanPool.lean",
+                    1,
+                    "axiom audit skipped: `lake` not found",
+                )
+            ]
     finally:
         temp_path.unlink(missing_ok=True)
 
@@ -678,13 +689,23 @@ def _check_project_declarations(
         temp_file.flush()
 
     try:
-        process = subprocess.run(
-            ["lake", "env", "lean", str(temp_path)],
-            cwd=root,
-            check=False,
-            capture_output=True,
-            text=True,
-        )
+        try:
+            process = subprocess.run(
+                ["lake", "env", "lean", str(temp_path)],
+                cwd=root,
+                check=False,
+                capture_output=True,
+                text=True,
+            )
+        except FileNotFoundError:
+            # `lake` not on PATH (sandboxed CI, contributor without Lean).
+            # Treat the same as `--skip-lean-axioms`: emit a single advisory
+            # error so callers know the check was skipped, rather than crash.
+            return [
+                _QualityError(
+                    path, 1, "project declarations check skipped: `lake` not found"
+                )
+            ]
     finally:
         temp_path.unlink(missing_ok=True)
 
diff --git a/python/tests/test_quality.py b/python/tests/test_quality.py
index c67d1c08e5..1cb4d93dfa 100644
--- a/python/tests/test_quality.py
+++ b/python/tests/test_quality.py
@@ -3,6 +3,7 @@
 from __future__ import annotations
 
 from pathlib import Path
+from unittest.mock import patch
 
 from lean_pool.quality import (
     _axiom_audit_missing,
@@ -190,6 +191,44 @@ def test_quality_check_accepts_project_card_after_imports(tmp_path: Path) -> Non
     assert not any("project card for p is out of date" in e.message for e in errors)
 
 
+def test_quality_check_falls_back_when_lake_missing(tmp_path: Path) -> None:
+    """A missing `lake` binary yields a single advisory error, not a crash.
+
+    The python_ci job runs without a Lean toolchain, so the subprocess
+    that invokes ``lake env lean`` raises ``FileNotFoundError``. The
+    quality module must catch that and emit a clear "skipped" message
+    rather than aborting the whole run.
+    """
+    _write_minimal_repo(tmp_path)
+    (tmp_path / "LeanPool.lean").write_text(
+        "import LeanPool.Basic\nimport LeanPool.MyProj\n"
+    )
+    card = (
+        "/-!\n"
+        "# Test Project\n"
+        "\n"
+        "Source: arxiv:1234.5678\n"
+        "Authors: Test Author\n"
+        "Status: verified\n"
+        "Main declarations: `hello`\n"
+        "Tags: test\n"
+        "-/\n"
+    )
+    (tmp_path / "LeanPool" / "MyProj.lean").write_text(
+        f"{HEADER}\nimport LeanPool.Basic\n\n{card}\ndef hello : Nat := 1\n"
+    )
+    _write_project_yaml(tmp_path, [{"slug": "p", "entry_module": "LeanPool.MyProj"}])
+
+    with patch(
+        "lean_pool.quality.subprocess.run",
+        side_effect=FileNotFoundError("[Errno 2] No such file or directory: 'lake'"),
+    ):
+        errors = run_checks(tmp_path)
+
+    messages = [error.message for error in errors]
+    assert any("`lake` not found" in message for message in messages)
+
+
 def test_quality_check_rejects_non_verified_status(tmp_path: Path) -> None:
     """Only `status: verified` projects may merge; `draft` is not accepted."""
     _write_minimal_repo(tmp_path)