diff --git a/Include/internal/pycore_object_deferred.h b/Include/internal/pycore_object_deferred.h
index c070d768b7d771..4156b6594974fa 100644
--- a/Include/internal/pycore_object_deferred.h
+++ b/Include/internal/pycore_object_deferred.h
@@ -16,15 +16,20 @@ extern "C" {
 // counting should be tracked by the GC so that they are eventually collected.
 extern void _PyObject_SetDeferredRefcount(PyObject *op);
 
+#ifdef Py_GIL_DISABLED
 static inline int
 _PyObject_HasDeferredRefcount(PyObject *op)
 {
-#ifdef Py_GIL_DISABLED
     return _PyObject_HAS_GC_BITS(op, _PyGC_BITS_DEFERRED);
+}
 #else
+static inline int
+_PyObject_HasDeferredRefcount(PyObject *Py_UNUSED(op))
+{
     return 0;
-#endif
 }
+#endif
+
 
 #ifdef __cplusplus
 }
diff --git a/Include/internal/pycore_stackref.h b/Include/internal/pycore_stackref.h
index 9495ccc8ac3889..abaa81f8678c2a 100644
--- a/Include/internal/pycore_stackref.h
+++ b/Include/internal/pycore_stackref.h
@@ -782,16 +782,22 @@ PyStackRef_LongCheck(_PyStackRef stackref)
     return PyLong_Check(PyStackRef_AsPyObjectBorrow(stackref));
 }
 
+#ifdef Py_GIL_DISABLED
 static inline void
 _PyThreadState_PushCStackRef(PyThreadState *tstate, _PyCStackRef *ref)
 {
-#ifdef Py_GIL_DISABLED
     _PyThreadStateImpl *tstate_impl = (_PyThreadStateImpl *)tstate;
     ref->next = tstate_impl->c_stack_refs;
     tstate_impl->c_stack_refs = ref;
-#endif
     ref->ref = PyStackRef_NULL;
 }
+#else
+static inline void
+_PyThreadState_PushCStackRef(PyThreadState *Py_UNUSED(tstate), _PyCStackRef *ref)
+{
+    ref->ref = PyStackRef_NULL;
+}
+#endif
 
 static inline void
 _PyThreadState_PushCStackRefNew(PyThreadState *tstate, _PyCStackRef *ref, PyObject *obj)
@@ -800,27 +806,39 @@ _PyThreadState_PushCStackRefNew(PyThreadState *tstate, _PyCStackRef *ref, PyObje
     ref->ref = PyStackRef_FromPyObjectNew(obj);
 }
 
+
+#ifdef Py_GIL_DISABLED
 static inline void
 _PyThreadState_PopCStackRef(PyThreadState *tstate, _PyCStackRef *ref)
 {
-#ifdef Py_GIL_DISABLED
     _PyThreadStateImpl *tstate_impl = (_PyThreadStateImpl *)tstate;
     assert(tstate_impl->c_stack_refs == ref);
     tstate_impl->c_stack_refs = ref->next;
-#endif
     PyStackRef_XCLOSE(ref->ref);
 }
 
 static inline _PyStackRef
 _PyThreadState_PopCStackRefSteal(PyThreadState *tstate, _PyCStackRef *ref)
 {
-#ifdef Py_GIL_DISABLED
     _PyThreadStateImpl *tstate_impl = (_PyThreadStateImpl *)tstate;
     assert(tstate_impl->c_stack_refs == ref);
     tstate_impl->c_stack_refs = ref->next;
-#endif
     return ref->ref;
 }
+#else
+static inline void
+_PyThreadState_PopCStackRef(PyThreadState *Py_UNUSED(tstate), _PyCStackRef *ref)
+{
+    PyStackRef_XCLOSE(ref->ref);
+}
+
+static inline _PyStackRef
+_PyThreadState_PopCStackRefSteal(PyThreadState *Py_UNUSED(tstate), _PyCStackRef *ref)
+{
+    return ref->ref;
+}
+#endif
+
 
 #ifdef Py_GIL_DISABLED
 
diff --git a/Include/slots.h b/Include/slots.h
index 4bf7bda0208a8d..3ef8768bbd26c3 100644
--- a/Include/slots.h
+++ b/Include/slots.h
@@ -42,7 +42,7 @@ struct PySlot {
 #define PySlot_STATIC_DATA(NAME, VALUE) \
     {.sl_id=(NAME), .sl_flags=PySlot_STATIC, .sl_ptr=(VALUE)}
 
-#define PySlot_END {0}
+#define PySlot_END {0, 0, {0}, {0}}
 
 
 // Macros without designated initializers (for C++11 and below):
diff --git a/Lib/test/test_cext/setup.py b/Lib/test/test_cext/setup.py
index 58bee3e255a4b3..52b63773c98cc0 100644
--- a/Lib/test/test_cext/setup.py
+++ b/Lib/test/test_cext/setup.py
@@ -21,6 +21,8 @@
 if not MSVC:
     # C compiler flags for GCC and clang
     BASE_CFLAGS = [
+        '-Wall',
+        '-Wextra',
         # The purpose of test_cext extension is to check that building a C
         # extension using the Python C API does not emit C compiler warnings.
         '-Werror',
@@ -71,6 +73,8 @@
 if not MSVC:
     # C++ compiler flags for GCC and clang
     CPPFLAGS = [
+        '-Wall',
+        '-Wextra',
         # gh-91321: The purpose of _testcppext extension is to check that building
         # a C++ extension using the Python C API does not emit C++ compiler
         # warnings