diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 9b73933..ab178a3 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -19,7 +19,7 @@ jobs:
             fail-fast: false
             matrix:
                 os: [ubuntu-latest]
-                python-version: ['3.10', '3.11']
+                python-version: ['3.9', '3.10', '3.11', '3.12']
                 pari-version: ['pari-2.11.4', 'pari-2.13.0', 'pari-2.15.4']
         env:
           LC_ALL: C
diff --git a/autogen/paths.py b/autogen/paths.py
index 3e8194f..e879464 100644
--- a/autogen/paths.py
+++ b/autogen/paths.py
@@ -15,12 +15,13 @@
 from __future__ import absolute_import, unicode_literals
 
 import os
+import shutil
+
 from glob import glob
-from distutils.spawn import find_executable
 
 
-# find_executable() returns None if nothing was found
-gppath = find_executable("gp")
+gppath = shutil.which("gp")
+
 if gppath is None:
     # This almost certainly won't work, but we need to put something here
     prefix = "."
diff --git a/cypari2/Py_SET_SIZE.h b/cypari2/Py_SET_SIZE.h
deleted file mode 100644
index 5f18ab0..0000000
--- a/cypari2/Py_SET_SIZE.h
+++ /dev/null
@@ -1,8 +0,0 @@
-#include "Python.h"
-
-#if (PY_MAJOR_VERSION == 3) && (PY_MINOR_VERSION < 9)
-// The function Py_SET_SIZE is defined starting with python 3.9.
-void Py_SET_SIZE(PyVarObject *o, Py_ssize_t size){
-    Py_SIZE(o) = size;
-}
-#endif
diff --git a/cypari2/convert.pyx b/cypari2/convert.pyx
index 7c2ed24..8d39c3c 100644
--- a/cypari2/convert.pyx
+++ b/cypari2/convert.pyx
@@ -54,14 +54,8 @@ from libc.math cimport INFINITY
 from .paridecl cimport *
 from .stack cimport new_gen, reset_avma
 from .string_utils cimport to_string, to_bytes
-
-cdef extern from *:
-    ctypedef struct PyLongObject:
-        digit* ob_digit
-
-cdef extern from "Py_SET_SIZE.h":
-    void Py_SET_SIZE(py_long o, Py_ssize_t size)
-
+from .pycore_long cimport (ob_digit, _PyLong_IsZero, _PyLong_IsNegative,
+        _PyLong_IsPositive, _PyLong_DigitCount, _PyLong_SetSignAndDigitCount)
 
 ########################################################################
 # Conversion PARI -> Python
@@ -424,7 +418,7 @@ cdef PyLong_FromINT(GEN g):
     cdef Py_ssize_t sizedigits_final = 0
 
     cdef py_long x = _PyLong_New(sizedigits)
-    cdef digit* D = x.ob_digit
+    cdef digit* D = ob_digit(x)
 
     cdef digit d
     cdef ulong w
@@ -452,10 +446,7 @@ cdef PyLong_FromINT(GEN g):
             sizedigits_final = i+1
 
     # Set correct size
-    if signe(g) > 0:
-        Py_SET_SIZE(x, sizedigits_final)
-    else:
-        Py_SET_SIZE(x, -sizedigits_final)
+    _PyLong_SetSignAndDigitCount(x, signe(g), sizedigits_final)
 
     return x
 
@@ -465,18 +456,18 @@ cdef PyLong_FromINT(GEN g):
 ########################################################################
 
 cdef GEN PyLong_AS_GEN(py_long x):
-    cdef const digit* D = x.ob_digit
+    cdef const digit* D = ob_digit(x)
 
     # Size of the input
     cdef size_t sizedigits
     cdef long sgn
-    if Py_SIZE(x) == 0:
+    if _PyLong_IsZero(x):
         return gen_0
-    elif Py_SIZE(x) > 0:
-        sizedigits = Py_SIZE(x)
+    elif _PyLong_IsPositive(x):
+        sizedigits = _PyLong_DigitCount(x)
         sgn = evalsigne(1)
     else:
-        sizedigits = -Py_SIZE(x)
+        sizedigits = _PyLong_DigitCount(x)
         sgn = evalsigne(-1)
 
     # Size of the output, in bits and in words
diff --git a/cypari2/pycore_long.h b/cypari2/pycore_long.h
new file mode 100644
index 0000000..ff1a73d
--- /dev/null
+++ b/cypari2/pycore_long.h
@@ -0,0 +1,98 @@
+#include "Python.h"
+#include <stdbool.h>
+
+#if PY_VERSION_HEX >= 0x030C00A5
+#define ob_digit(o)  (((PyLongObject*)o)->long_value.ob_digit)
+#else
+#define ob_digit(o)  (((PyLongObject*)o)->ob_digit)
+#endif
+
+#if PY_VERSION_HEX >= 0x030C00A7
+// taken from cpython:Include/internal/pycore_long.h @ 3.12
+
+/* Long value tag bits:
+ * 0-1: Sign bits value = (1-sign), ie. negative=2, positive=0, zero=1.
+ * 2: Reserved for immortality bit
+ * 3+ Unsigned digit count
+ */
+#define SIGN_MASK 3
+#define SIGN_ZERO 1
+#define SIGN_NEGATIVE 2
+#define NON_SIZE_BITS 3
+
+static inline bool
+_PyLong_IsZero(const PyLongObject *op)
+{
+    return (op->long_value.lv_tag & SIGN_MASK) == SIGN_ZERO;
+}
+
+static inline bool
+_PyLong_IsNegative(const PyLongObject *op)
+{
+    return (op->long_value.lv_tag & SIGN_MASK) == SIGN_NEGATIVE;
+}
+
+static inline bool
+_PyLong_IsPositive(const PyLongObject *op)
+{
+    return (op->long_value.lv_tag & SIGN_MASK) == 0;
+}
+
+static inline Py_ssize_t
+_PyLong_DigitCount(const PyLongObject *op)
+{
+    assert(PyLong_Check(op));
+    return op->long_value.lv_tag >> NON_SIZE_BITS;
+}
+
+#define TAG_FROM_SIGN_AND_SIZE(sign, size) ((1 - (sign)) | ((size) << NON_SIZE_BITS))
+
+static inline void
+_PyLong_SetSignAndDigitCount(PyLongObject *op, int sign, Py_ssize_t size)
+{
+    assert(size >= 0);
+    assert(-1 <= sign && sign <= 1);
+    assert(sign != 0 || size == 0);
+    op->long_value.lv_tag = TAG_FROM_SIGN_AND_SIZE(sign, (size_t)size);
+}
+
+#else
+// fallback for < 3.12
+
+static inline bool
+_PyLong_IsZero(const PyLongObject *op)
+{
+    return Py_SIZE(op) == 0;
+}
+
+static inline bool
+_PyLong_IsNegative(const PyLongObject *op)
+{
+    return Py_SIZE(op) < 0;
+}
+
+static inline bool
+_PyLong_IsPositive(const PyLongObject *op)
+{
+    return Py_SIZE(op) > 0;
+}
+
+static inline Py_ssize_t
+_PyLong_DigitCount(const PyLongObject *op)
+{
+    Py_ssize_t size = Py_SIZE(op);
+    return size < 0 ? -size : size;
+}
+
+static inline void
+_PyLong_SetSignAndDigitCount(PyLongObject *op, int sign, Py_ssize_t size)
+{
+#if (PY_MAJOR_VERSION == 3) && (PY_MINOR_VERSION < 9)
+// The function Py_SET_SIZE is defined starting with python 3.9.
+    Py_SIZE(o) = size;
+#else
+    Py_SET_SIZE(op, sign < 0 ? -size : size);
+#endif
+}
+
+#endif
diff --git a/cypari2/pycore_long.pxd b/cypari2/pycore_long.pxd
new file mode 100644
index 0000000..41de637
--- /dev/null
+++ b/cypari2/pycore_long.pxd
@@ -0,0 +1,9 @@
+from cpython.longintrepr cimport py_long, digit
+
+cdef extern from "pycore_long.h":
+    digit* ob_digit(py_long o)
+    bint _PyLong_IsZero(py_long o)
+    bint _PyLong_IsNegative(py_long o)
+    bint _PyLong_IsPositive(py_long o)
+    Py_ssize_t _PyLong_DigitCount(py_long o)
+    void _PyLong_SetSignAndDigitCount(py_long o, int sign, Py_ssize_t size)