diff --git a/Lib/test/test_code.py b/Lib/test/test_code.py
index 631e5fd2499b13..f54703cf37b2de 100644
--- a/Lib/test/test_code.py
+++ b/Lib/test/test_code.py
@@ -1251,10 +1251,15 @@ def __hash__(self):
         class MyInt(int):
             pass
 
+        class MyComplex(complex):
+            pass
+
         code = compile("a = 1", "<string>", "exec")
-        code = code.replace(co_consts=(1, Unhashable(), MyInt(1), MyInt(1)))
+        code = code.replace(co_consts=(1, Unhashable(), MyInt(1), MyInt(1),
+                                       MyComplex(1j)))
         self.assertIsInstance(code.co_consts[1], Unhashable)
         self.assertEqual(code.co_consts[2], code.co_consts[3])
+        self.assertFalse(sys._is_immortal(code.co_consts[4]))
 
 
 class CodeWeakRefTest(unittest.TestCase):
diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2026-10-20-00-00-00.gh-issue-159739.d76e6d.rst b/Misc/NEWS.d/next/Core_and_Builtins/2026-10-20-00-00-00.gh-issue-159739.d76e6d.rst
new file mode 100644
index 00000000000000..a027883426be19
--- /dev/null
+++ b/Misc/NEWS.d/next/Core_and_Builtins/2026-10-20-00-00-00.gh-issue-159739.d76e6d.rst
@@ -0,0 +1,2 @@
+Prevent free-threaded builds from interning and immortalizing complex
+subclasses in code object constants.
diff --git a/Objects/codeobject.c b/Objects/codeobject.c
index 724243d2b8cfae..eb390ab24ec13e 100644
--- a/Objects/codeobject.c
+++ b/Objects/codeobject.c
@@ -174,7 +174,7 @@ should_immortalize_constant(PyObject *v)
                 _Py_IsImmortal(slice->step));
     }
     return (PyLong_CheckExact(v) || PyFloat_CheckExact(v) ||
-            PyComplex_Check(v) || PyBytes_CheckExact(v));
+            PyComplex_CheckExact(v) || PyBytes_CheckExact(v));
 }
 #endif