diff --git a/src/runez/_inspect.py b/src/runez/_inspect.py
index bf91c5e..363e2cc 100644
--- a/src/runez/_inspect.py
+++ b/src/runez/_inspect.py
@@ -6,7 +6,7 @@
 
 
 def simple_inspection():
-    # `Py_GIL_DISABLED` is None on regular CPython builds and 1 on freethreaded builds — normalize to bool
+    # `Py_GIL_DISABLED` is None on regular CPython builds and 1 on freethreaded builds, normalize to bool
     freethreading = bool(sysconfig.get_config_var("Py_GIL_DISABLED"))
     return {"version": ".".join(str(s) for s in sys.version_info[:3]), "machine": platform.machine(), "freethreading": freethreading}
 
diff --git a/tests/test_pyenv.py b/tests/test_pyenv.py
index 52e18aa..5b8eb83 100644
--- a/tests/test_pyenv.py
+++ b/tests/test_pyenv.py
@@ -243,6 +243,17 @@ def test_inspect():
     assert '"version":' in r.output
 
 
+def test_inspect_is_ascii_only():
+    # `_inspect.py` may be invoked by arbitrary (possibly Py2) python binaries, so it must stay
+    # ASCII-only: a stray non-ASCII byte raises SyntaxError under Py2 unless an encoding is declared.
+    import runez._inspect
+
+    inspect_path = runez.to_path(runez._inspect.__file__)
+    src_text = inspect_path.read_text()
+    src_bytes = inspect_path.read_bytes()
+    assert src_bytes.decode("ascii") == src_text  # raises UnicodeDecodeError if any non-ASCII byte sneaks in
+
+
 def test_invoker():
     import runez.pyenv