diff --git a/.github/workflows/build-and-test.yaml b/.github/workflows/build-and-test.yaml
new file mode 100644
index 0000000..c8cce1b
--- /dev/null
+++ b/.github/workflows/build-and-test.yaml
@@ -0,0 +1,43 @@
+name: Build/Test
+
+on:
+  workflow_call:
+  workflow_dispatch:
+    inputs:
+      part:
+        required: false
+        default: ''
+
+jobs:
+  build:
+    name: Build the library and run tests
+    strategy:
+      matrix:
+        os: [ubuntu-latest, ubuntu-24.04, ubuntu-22.04, ubuntu-24.04-arm]
+      fail-fast: false
+    runs-on: ${{ matrix.os }}
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Install dependencies
+        run: |
+          if [[ "${{ matrix.os }}" =~ "ubuntu" ]]; then
+            sudo apt update
+            sudo apt install -y python3-pytest cython3
+          else
+            brew install pytest python-setuptools
+            git clone --single-branch --branch 3.1.x https://github.com/cython/cython.git
+            cd cython
+            sudo python3 setup.py install
+            cd ..
+          fi
+
+      - name: Build and install library
+        run: |
+          python3 setup.py build_ext
+          sudo python3 setup.py install
+
+      - name: Run tests
+        run: |
+          pytest-3 .
diff --git a/.github/workflows/pr.yaml b/.github/workflows/pr.yaml
new file mode 100644
index 0000000..0689df6
--- /dev/null
+++ b/.github/workflows/pr.yaml
@@ -0,0 +1,8 @@
+name: PR
+
+on:
+  pull_request:
+
+jobs:
+  build:
+    uses: ./.github/workflows/build-and-test.yaml
diff --git a/setup.py b/setup.py
index ef9f7cf..c62861c 100644
--- a/setup.py
+++ b/setup.py
@@ -3,7 +3,7 @@
 import shutil
 import sys
 from setuptools import setup, Extension
-from setuptools.command.build import build
+from setuptools.command.build_ext import build_ext
 from Cython.Build import cythonize
 
 extension_modules = [
@@ -21,7 +21,7 @@
 with open (os.path.join (base_path, "requirements.txt")) as reqs:
   requirements = reqs.read ()
 
-class CustomBuild(build):
+class CustomBuild(build_ext):
   def run(self):
     super().run()
     suffix = '.dll' if 'win' in sys.platform.lower() else '.so'
@@ -45,7 +45,7 @@ def run(self):
   test_suite = "tests",
   install_requires = requirements,
   zip_safe = False,
-  cmdclass = {'build': CustomBuild},
+  cmdclass = {'build_ext': CustomBuild},
   ext_modules = cythonize (extension_modules, include_path = include_dirs,
                            language_level = 3, annotate = True,
                            compiler_directives = {'embedsignature': True}),
diff --git a/zser/defs.h b/zser/defs.h
index e976192..8e4116b 100644
--- a/zser/defs.h
+++ b/zser/defs.h
@@ -27,6 +27,11 @@ STR_NEW (unsigned int code, size_t len, const void *ptr)
   b->length = len;
   b->hash = -1;
   b->state.compact = 0;
+
+#if PY_MINOR_VERSION <= 11
+  b->state.ready = 1;
+#endif
+
   b->state.interned = 0;   // SSTATE_NOT_INTERNED
   if (code == 3)
     {
@@ -39,6 +44,14 @@ STR_NEW (unsigned int code, size_t len, const void *ptr)
     {
       b->state.ascii = 0;
       b->state.kind = code;
+
+#if PY_MINOR_VERSION <= 11
+      if (code == sizeof (wchar_t))
+        {
+          b->wstr = (wchar_t *)p->data.any;
+          c->wstr_length = b->length;
+        }
+#endif
     }
 
   return ((PyObject *)p);
@@ -52,6 +65,9 @@ STR_FINI (PyObject *obj)
   PyUnicodeObject *p = (PyUnicodeObject *)obj;
   p->data.any = NULL;
   p->_base.utf8 = NULL;
+#if PY_MINOR_VERSION <= 11
+  p->_base._base.wstr = NULL;
+#endif
 }
 
 static int
diff --git a/zser/zser.pyx b/zser/zser.pyx
index d7f6ec5..e29e5d4 100644
--- a/zser/zser.pyx
+++ b/zser/zser.pyx
@@ -62,7 +62,7 @@ cdef size_t[6] _BASIC_SIZES = [sizeof (char), sizeof (short),
 
 # Basic types that may be stored inline in lists, sets, dicts and descriptors.
 ctypedef fused cnum:
-  char
+  signed char
   unsigned char
   short
   unsigned short
@@ -105,7 +105,7 @@ cdef union fn_caster:
 # Special object used for detecting misses in dict lookups.
 cdef object _SENTINEL = object ()
 
-cdef inline bint _is_inline_code (unsigned int code) noexcept:
+cdef inline bint _is_inline_code (unsigned int code) :
   return code <= tpcode.FLOAT64
 
 cdef inline size_t _get_padding (size_t off, size_t size):
@@ -131,7 +131,7 @@ cdef _pack_cnum (Packer xm, int code, cnum value, bint tag):
 
 def _pack_int (Packer xm, value, tag):
   if INT8_MIN <= value <= INT8_MAX:
-    _pack_cnum[char] (xm, tpcode.INT8, value, tag)
+    _pack_cnum[cy.schar] (xm, tpcode.INT8, value, tag)
   elif INT16_MIN <= value <= INT16_MAX:
     _pack_cnum[short] (xm, tpcode.INT16, value, tag)
   elif INT32_MIN <= value <= INT32_MAX:
@@ -834,7 +834,7 @@ cdef class Proxy:
     cdef unsigned int ilen
 
     if code == tpcode.INT8:
-      return _cnum_unpack[char] (self, offset, 0)
+      return _cnum_unpack[cy.schar] (self, offset, 0)
     elif code == tpcode.INT16:
       return _cnum_unpack[short] (self, offset, 0)
     elif code == tpcode.INT32:
@@ -921,7 +921,7 @@ cdef class Proxy:
 cdef inline object _builtin_read (void *buf, Py_ssize_t pos,
                                   unsigned int code):
   if code == tpcode.INT8:
-    return (<char *>buf)[pos]
+    return (<signed char *>buf)[pos]
   elif code == tpcode.INT16:
     return (<short *>buf)[pos]
   elif code == tpcode.INT32:
@@ -935,7 +935,7 @@ cdef inline object _builtin_read (void *buf, Py_ssize_t pos,
 cdef inline void _builtin_write (void *buf, Py_ssize_t pos,
                                  object obj, unsigned int code):
   if code == tpcode.INT8:
-    (<int *>buf)[pos] = obj
+    (<signed char *>buf)[pos] = obj
   elif code == tpcode.INT16:
     (<short *>buf)[pos] = obj
   elif code == tpcode.INT32:
@@ -989,7 +989,7 @@ cdef inline object _builtin_aadd_impl (cnum *ptr, object val):
 cdef inline object _builtin_aadd (void *buf, Py_ssize_t pos,
                                   object val, unsigned int code):
   if code == tpcode.INT8:
-    return _builtin_aadd_impl[char] (<char *>buf + pos, val)
+    return _builtin_aadd_impl[cy.schar] (<signed char *>buf + pos, val)
   elif code == tpcode.INT16:
     return _builtin_aadd_impl[short] (<short *>buf + pos, val)
   elif code == tpcode.INT32:
@@ -1004,7 +1004,7 @@ cdef inline object _builtin_aadd (void *buf, Py_ssize_t pos,
 cdef object _builtin_acas (void *buf, Py_ssize_t pos, object exp,
                            object nval, unsigned int code):
   if code == tpcode.INT8:
-    return _builtin_acas_impl[char] (<char *>buf + pos, exp, nval)
+    return _builtin_acas_impl[cy.schar] (<signed char *>buf + pos, exp, nval)
   elif code == tpcode.INT16:
     return _builtin_acas_impl[short] (<short *>buf + pos, exp, nval)
   elif code == tpcode.INT32:
@@ -1538,13 +1538,13 @@ cdef _ProxyStr_mul (x, y):
 TYPE_PATCH (<PyTypeObject *>ProxyStr, _ProxyStr_add,
             _ProxyStr_mod, _ProxyStr_mul)
 
-cdef inline size_t _rotate_hash (size_t code, size_t nbits) noexcept:
+cdef inline size_t _rotate_hash (size_t code, size_t nbits) :
   return (code << nbits) | (code >> (sizeof (size_t) * 8 - nbits))
 
-cdef inline size_t _mix_hash (size_t h1, size_t h2) noexcept:
+cdef inline size_t _mix_hash (size_t h1, size_t h2) :
   return _rotate_hash (h1, 5) ^ h2
 
-cdef inline size_t _hash_buf (const void *ptr, size_t nbytes) noexcept:
+cdef inline size_t _hash_buf (const void *ptr, size_t nbytes) :
   cdef size_t ret
 
   ret = nbytes
@@ -1554,7 +1554,7 @@ cdef inline size_t _hash_buf (const void *ptr, size_t nbytes) noexcept:
 
   return ret if ret != 0 else WORD_MAX
 
-cdef inline size_t _hash_str (str sobj) noexcept:
+cdef inline size_t _hash_str (str sobj) :
   cdef unsigned int kind
 
   kind = STR_KIND (sobj)
@@ -1562,7 +1562,7 @@ cdef inline size_t _hash_str (str sobj) noexcept:
     kind = 1
   return _hash_buf (PyUnicode_DATA (sobj), len (sobj) * kind)
 
-cdef inline size_t _hash_flt (double flt) noexcept:
+cdef inline size_t _hash_flt (double flt) :
   cdef double ipart
 
   if modf (flt, &ipart) == 0:
@@ -1624,7 +1624,7 @@ def xhash (obj, seed = 0):
 
 #######################################
 
-cdef inline Py_ssize_t _cfloat_diff (cfloat x, cfloat y) noexcept:
+cdef inline Py_ssize_t _cfloat_diff (cfloat x, cfloat y) :
   cdef double ret
 
   ret = x - y
@@ -1706,7 +1706,7 @@ cdef int _cnum_find_sorted (const unsigned char *ptr, size_t n, obj,
 
 @cy.cdivision (True)
 @cy.nogil
-cdef size_t _find_hidx (hidx_type hidxs, size_t hval, size_t n) noexcept:
+cdef size_t _find_hidx (hidx_type hidxs, size_t hval, size_t n) :
   cdef size_t i, step, tmp
 
   i = 0
@@ -1779,7 +1779,7 @@ cdef size_t _find_obj_by_hidx (hidx_type hidxs, size_t ix, size_t n,
 ################################
 # Functions on sets.
 
-cdef inline bint _cnum_lt (cnum x, cnum y) noexcept:
+cdef inline bint _cnum_lt (cnum x, cnum y) :
   if cnum is double or cnum is float:
     return _cfloat_diff (x, y) < 0
   else:
@@ -1920,7 +1920,7 @@ cdef class ProxySet:
       p2 = <const unsigned char *> (ix2.proxy.base + ix2.offset)
 
       if ix1.code == tpcode.INT8:
-        _cnum_set_union[char] (p1, ix1.size, p2, ix2.size, out, 0)
+        _cnum_set_union[cy.schar] (p1, ix1.size, p2, ix2.size, out, 0)
       elif ix1.code == tpcode.INT16:
         _cnum_set_union[short] (p1, ix1.size, p2, ix2.size, out, 0)
       elif ix1.code == tpcode.INT32:
@@ -1950,7 +1950,7 @@ cdef class ProxySet:
       p2 = <const unsigned char *> (ix2.proxy.base + ix2.offset)
 
       if ix1.code == tpcode.INT8:
-        _cnum_set_intersection[char] (p1, ix1.size, p2, ix2.size, out, 0)
+        _cnum_set_intersection[cy.schar] (p1, ix1.size, p2, ix2.size, out, 0)
       elif ix1.code == tpcode.INT16:
         _cnum_set_intersection[short] (p1, ix1.size, p2, ix2.size, out, 0)
       elif ix1.code == tpcode.INT32:
@@ -1980,7 +1980,7 @@ cdef class ProxySet:
       p2 = <const unsigned char *> (ix2.proxy.base + ix2.offset)
 
       if ix1.code == tpcode.INT8:
-        _cnum_set_difference[char] (p1, ix1.size, p2, ix2.size, out, 0)
+        _cnum_set_difference[cy.schar] (p1, ix1.size, p2, ix2.size, out, 0)
       elif ix1.code == tpcode.INT16:
         _cnum_set_difference[short] (p1, ix1.size, p2, ix2.size, out, 0)
       elif ix1.code == tpcode.INT32:
@@ -2010,7 +2010,7 @@ cdef class ProxySet:
       p2 = <const unsigned char *> (ix2.proxy.base + ix2.offset)
 
       if ix1.code == tpcode.INT8:
-        _cnum_set_symdiff[char] (p1, ix1.size, p2, ix2.size, out, 0)
+        _cnum_set_symdiff[cy.schar] (p1, ix1.size, p2, ix2.size, out, 0)
       elif ix1.code == tpcode.INT16:
         _cnum_set_symdiff[short] (p1, ix1.size, p2, ix2.size, out, 0)
       elif ix1.code == tpcode.INT32:
@@ -2042,7 +2042,7 @@ cdef class ProxySet:
     ptr = <const unsigned char *> (proxy.base + indices.offset)
 
     if code == tpcode.INT8:
-      return _cnum_find_sorted[char] (ptr, n, value, 0, 0)
+      return _cnum_find_sorted[cy.schar] (ptr, n, value, 0, 0)
     elif code == tpcode.INT16:
       return _cnum_find_sorted[short] (ptr, n, value, 0, 0)
     elif code == tpcode.INT32:
@@ -2211,7 +2211,7 @@ cdef class ProxySet:
       if ix1.size > ix2.size:
         ret = False
       elif self.indices.code == tpcode.INT8:
-        ret = _cnum_set_includes[char] (p2, ix2.size, p1, ix1.size, 0)
+        ret = _cnum_set_includes[cy.schar] (p2, ix2.size, p1, ix1.size, 0)
       elif self.indices.code == tpcode.INT16:
         ret = _cnum_set_includes[short] (p2, ix2.size, p1, ix1.size, 0)
       elif self.indices.code == tpcode.INT32: