diff --git a/pythoncapi_compat.h b/pythoncapi_compat.h
index e26185c..99970f6 100644
--- a/pythoncapi_compat.h
+++ b/pythoncapi_compat.h
@@ -1569,6 +1569,11 @@ static inline int PyLong_IsZero(PyObject *obj)
 
 // gh-124502 added PyUnicode_Equal() to Python 3.14.0a0
 #if PY_VERSION_HEX < 0x030E00A0
+
+#if PY_VERSION_HEX >= 0x030d0000 && !defined(PYPY_VERSION)
+PyAPI_FUNC(int) _PyUnicode_Equal(PyObject *str1, PyObject *str2);
+#endif
+
 static inline int PyUnicode_Equal(PyObject *str1, PyObject *str2)
 {
     if (!PyUnicode_Check(str1)) {
@@ -1583,8 +1588,6 @@ static inline int PyUnicode_Equal(PyObject *str1, PyObject *str2)
     }
 
 #if PY_VERSION_HEX >= 0x030d0000 && !defined(PYPY_VERSION)
-    PyAPI_FUNC(int) _PyUnicode_Equal(PyObject *str1, PyObject *str2);
-
     return _PyUnicode_Equal(str1, str2);
 #elif PY_VERSION_HEX >= 0x03060000 && !defined(PYPY_VERSION)
     return _PyUnicode_EQ(str1, str2);
@@ -1607,11 +1610,14 @@ static inline PyObject* PyBytes_Join(PyObject *sep, PyObject *iterable)
 
 
 #if PY_VERSION_HEX < 0x030E00A0
+
+#if PY_VERSION_HEX >= 0x03000000 && !defined(PYPY_VERSION)
+PyAPI_FUNC(Py_hash_t) _Py_HashBytes(const void *src, Py_ssize_t len);
+#endif
+
 static inline Py_hash_t Py_HashBuffer(const void *ptr, Py_ssize_t len)
 {
 #if PY_VERSION_HEX >= 0x03000000 && !defined(PYPY_VERSION)
-    PyAPI_FUNC(Py_hash_t) _Py_HashBytes(const void *src, Py_ssize_t len);
-
     return _Py_HashBytes(ptr, len);
 #else
     Py_hash_t hash;
@@ -1948,11 +1954,14 @@ PyLongWriter_Finish(PyLongWriter *writer)
 
 // gh-127350 added Py_fopen() and Py_fclose() to Python 3.14a4
 #if PY_VERSION_HEX < 0x030E00A4
+
+#if 0x030400A2 <= PY_VERSION_HEX && !defined(PYPY_VERSION)
+PyAPI_FUNC(FILE*) _Py_fopen_obj(PyObject *path, const char *mode);
+#endif
+
 static inline FILE* Py_fopen(PyObject *path, const char *mode)
 {
 #if 0x030400A2 <= PY_VERSION_HEX && !defined(PYPY_VERSION)
-    PyAPI_FUNC(FILE*) _Py_fopen_obj(PyObject *path, const char *mode);
-
     return _Py_fopen_obj(path, mode);
 #else
     FILE *f;
@@ -2664,6 +2673,10 @@ PyUnstable_Unicode_GET_CACHED_HASH(PyObject *op)
 // to make objects immortal until 3.14 which has _Py_SetImmortal(). Since
 // immortal objects are primarily needed for free-threading, this API is implemented
 // for 3.14 using _Py_SetImmortal() and uses private macros on 3.13.
+#if 0x030E0000 <= PY_VERSION_HEX
+PyAPI_FUNC(void) _Py_SetImmortal(PyObject *op);
+#endif
+
 static inline int
 PyUnstable_SetImmortal(PyObject *op)
 {
@@ -2672,7 +2685,6 @@ PyUnstable_SetImmortal(PyObject *op)
         return 0;
     }
 #if 0x030E0000 <= PY_VERSION_HEX
-    PyAPI_FUNC(void) _Py_SetImmortal(PyObject *op);
     _Py_SetImmortal(op);
 #else
     // Python 3.13 doesn't export _Py_SetImmortal() function
diff --git a/tests/setup.py b/tests/setup.py
index e394bce..b25bc8d 100755
--- a/tests/setup.py
+++ b/tests/setup.py
@@ -32,9 +32,6 @@
         '-Wall', '-Wextra',
         # Extra warnings
         '-Wconversion',
-        # /usr/lib64/pypy3.7/include/pyport.h:68:20: error: redefinition of typedef
-        # 'Py_hash_t' is a C11 feature
-        '-Wno-typedef-redefinition',
         # Formatting checks
         '-Wformat',
         '-Wformat-nonliteral',
@@ -47,6 +44,14 @@
         # Treat all compiler warnings as compiler errors
         '/WX',
     ))
+    # Python 3.11 and older emits C4100 "unreferenced parameter" warnings
+    # on Py_UNUSED() parameters. Py_UNUSED() was modified in Python 3.12
+    # to support MSVC.
+    if sys.version_info >= (3, 12):
+        COMMON_FLAGS.extend((
+            # Display warnings level 1 to 4
+            '/W4',
+        ))
     CFLAGS = list(COMMON_FLAGS)
 CXXFLAGS = list(COMMON_FLAGS)