@@ -103,6 +103,7 @@ jobs:
           - 3.7
           - 3.8
           - 3.9
+          - 3.10.0-rc.2
         os: [ubuntu-20.04, macos-latest]
         exclude:
           - os: macos-latest
@@ -189,6 +190,7 @@ jobs:
           - 3.7
           - 3.8
           - 3.9
+          - 3.10.0-rc.2
         os: [ubuntu-20.04, macos-latest]
         exclude:
           - os: macos-latest
 
@@ -33,6 +33,7 @@ for PYBIN in /opt/python/*/bin; do
        [[ "${PYBIN}" == *"cp36"* ]] || \
        [[ "${PYBIN}" == *"cp37"* ]] || \
        [[ "${PYBIN}" == *"cp38"* ]] || \
+       [[ "${PYBIN}" == *"cp310"* ]] || \
        [[ "${PYBIN}" == *"cp39"* ]]; then
         "${PYBIN}/pip" install -e /io/
         "${PYBIN}/pip" wheel /io/ -w wheelhouse/
 
@@ -10,7 +10,7 @@ with-windows = false
 with-pypy = true
 with-legacy-python = true
 with-sphinx-doctests = false
-with-future-python = false
+with-future-python = true
 
 [tox]
 use-flake8 = false
 
@@ -5,7 +5,7 @@
 2.1.1 (unreleased)
 ==================
 
-- Nothing changed yet.
+- Add support for Python 3.10.
 
 
 2.1.0 (2021-09-24)
 
@@ -21,6 +21,10 @@ environment:
     - python: 38-x64
     - python: 39
     - python: 39-x64
+    # `multibuild` cannot install non-final versions as they are not on
+    # ftp.python.org, so we skip Python 3.10 until its final release:
+    # - python: 310
+    # - python: 310-x64
 
 install:
   - "SET PYTHONVERSION=%PYTHON%"
 
@@ -67,6 +67,7 @@ def read(fname):
         'Programming Language :: Python :: 3.7',
         'Programming Language :: Python :: 3.8',
         'Programming Language :: Python :: 3.9',
+        'Programming Language :: Python :: 3.10',
         'Programming Language :: Python :: Implementation :: CPython',
         'Programming Language :: Python :: Implementation :: PyPy',
         'Programming Language :: Python :: Implementation :: Jython',
 
@@ -4,6 +4,28 @@
 PyDoc_STRVAR(pickle_module_doc,
 "Optimized C implementation for the Python pickle module.");
 
+
+#if (PY_VERSION_HEX >= 0x30A00B1) /* 3.10.0b1 */
+#ifndef Py_SIZE
+#define Py_SIZE(ob) (((PyVarObject*)(ob))->ob_size)
+#endif
+#define _PyUnicode_AsStringAndSize PyUnicode_AsUTF8AndSize
+/**
+ * The function ``_PyObject_LookupAttrId`` function replaces the combo of
+ * ``_PyObject_HasAttrId`` followed by ``_PyObject_GetAttrId``; our code isn't
+ * structured to take advantage of that, so for now we throw away the
+ * resulting attribute value and continue to make the extra ``Get`` call.
+ */
+static int _PyObject_HasAttrId(PyObject* obj, void* id)
+{
+    int result;
+    PyObject* attr_val;
+    result = _PyObject_LookupAttrId(obj, id, &attr_val);
+    Py_XDECREF(attr_val);
+    return result;
+}
+#endif
+
 /* Bump this when new opcodes are added to the pickle protocol. */
 enum {
     HIGHEST_PROTOCOL = 3,
@@ -1633,7 +1655,7 @@ save_long(PicklerObject *self, PyObject *obj)
             goto error;
     }
     else {
-        char *string;
+        const char *string;
 
         /* proto < 2: write the repr and newline.  This is quadratic-time (in
            the number of digits), in both directions.  We add a trailing 'L'
@@ -2929,7 +2951,7 @@ save_pers(PicklerObject *self, PyObject *obj, PyObject *func)
         }
         else {
             PyObject *pid_str = NULL;
-            char *pid_ascii_bytes;
+            const char *pid_ascii_bytes;
             Py_ssize_t size;
 
             pid_str = PyObject_Str(pid);
 
@@ -1,14 +1,16 @@
 import io
+import os
 import unittest
 import sys
 import copyreg
 import weakref
+import tempfile
 from http.cookies import SimpleCookie
 from zodbpickle import pickle_3 as pickle
 from zodbpickle import pickletools_3 as pickletools
 
 from test.support import (
-    TestFailed, TESTFN, run_with_locale,
+    TestFailed, run_with_locale,
     _2G, _4G, bigmemtest,
     )
 
@@ -41,6 +43,8 @@ def wrapper(*args, **kwargs):
 
 ascii_char_size = 1
 
+fd, TESTFN = tempfile.mkstemp('.pickletester_3')
+os.close(fd)
 
 # Return True if opcode code appears in the pickle, else False.
 def opcode_in_pickle(code, pickle):
 
@@ -10,6 +10,7 @@ envlist =
     py37,py37-pure
     py38,py38-pure
     py39,py39-pure
+    py310,py310-pure
     pypy
     pypy3
     coverage