diff --git a/gmp.c b/gmp.c
index 65fe44b5..ff5ab5e8 100644
--- a/gmp.c
+++ b/gmp.c
@@ -135,7 +135,7 @@ MPZ_to_str(MPZ_Object *u, int base, int options)
 static MPZ_Object *
 MPZ_from_str(PyObject *obj, int base)
 {
-    const char *str = PyUnicode_AsUTF8(obj);
+    const char *str = PyUnicode_AsUTF8AndSize(obj, NULL);
 
     if (!str) {
         return NULL; /* LCOV_EXCL_LINE */
@@ -157,6 +157,7 @@ MPZ_from_str(PyObject *obj, int base)
     }
     else if (ret == ZZ_BUF) {
         /* LCOV_EXCL_START */
+        Py_DECREF(res);
         PyErr_SetString(PyExc_OverflowError,
                         "too many digits in integer");
         return NULL;
@@ -438,15 +439,8 @@ new_impl(PyTypeObject *Py_UNUSED(type), PyObject *arg, PyObject *base_arg)
     }
 str:
     if (PyUnicode_Check(arg)) {
-        PyObject *asciistr = gmp_PyUnicode_TransformDecimalAndSpaceToASCII(arg);
-
-        if (!asciistr) {
-            return NULL; /* LCOV_EXCL_LINE */
-        }
-
-        PyObject *res = (PyObject *)MPZ_from_str(asciistr, base);
+        PyObject *res = (PyObject *)MPZ_from_str(arg, base);
 
-        Py_DECREF(asciistr);
         return res;
     }
     else if (PyByteArray_Check(arg) || PyBytes_Check(arg)) {
@@ -1644,7 +1638,7 @@ The signed argument indicates whether two’s complement is used."},
 
 PyDoc_STRVAR(mpz_doc,
              "mpz(number=0, /)\nmpz(string, /, base=10)\n\n\
-Convert a number or a string to an integer.  If numeric argument is not\n\
+Convert a number or an ASCII string to an integer.  If numeric argument is not\n\
 an int subclass, return mpz(int(number)).\n\n\
 If argument is not a number or if base is given, then it must be a string,\n\
 bytes, or bytearray instance representing an integer literal in the\n\
diff --git a/tests/test_mpz.py b/tests/test_mpz.py
index 146987a6..e0a07744 100644
--- a/tests/test_mpz.py
+++ b/tests/test_mpz.py
@@ -270,16 +270,13 @@ def test_mpz_interface():
     with pytest.raises(ValueError, match="invalid literal"):
         mpz(" ")
     with pytest.raises(ValueError, match="invalid literal"):
-        mpz("ыыы")
+        mpz("qqq")
     assert mpz() == mpz(0) == 0
     assert mpz("  -123") == -123
     assert mpz("123  ") == 123
     assert mpz("    -123  ") == -123
     assert mpz("+123") == 123
-    assert mpz("١٢٣٤") == 1234  # unicode decimal digits
-    assert mpz("١23") == 123
     assert mpz("\t123") == 123
-    assert mpz("\xa0123") == 123
     assert mpz("-010") == -10
     assert mpz("-10") == -10
     assert mpz("0b_10", 0) == 2
@@ -950,12 +947,14 @@ def test_from_bytes_interface():
 @example(1<<116)
 @example(646541478744828163276576707651635923929979156076518566789121)
 @example((0xfffffffffffff8<<(242*4)) + (1<<970))
+@example(0xa<<10000)
 def test_to_float(x):
     mx = mpz(x)
     try:
         fx = float(x)
     except OverflowError:
-        pytest.raises(OverflowError, lambda: float(mx))
+        with pytest.raises(OverflowError):
+            float(mx)
     else:
         assert str(float(mx)) == str(fx)
 
diff --git a/utils.c b/utils.c
index 7b1bde36..e5cae2ea 100644
--- a/utils.c
+++ b/utils.c
@@ -61,47 +61,3 @@ gmp_parse_pyargs(const gmp_pyargs *fnargs, Py_ssize_t argidx[],
     }
     return 0;
 }
-
-/* copied from CPython internals */
-PyObject *
-gmp_PyUnicode_TransformDecimalAndSpaceToASCII(PyObject *unicode)
-{
-    assert(PyUnicode_Check(unicode));
-    if (PyUnicode_IS_ASCII(unicode)) {
-        return Py_NewRef(unicode);
-    }
-
-    Py_ssize_t len = PyUnicode_GetLength(unicode);
-    PyObject *result = PyUnicode_New(len, 127);
-
-    if (result == NULL) {
-        return NULL; /* LCOV_EXCL_LINE */
-    }
-
-    Py_UCS1 *out = PyUnicode_1BYTE_DATA(result);
-    int kind = (int)PyUnicode_KIND(unicode); /* oracle/graalpython#580 */
-    const void *data = PyUnicode_DATA(unicode);
-
-    for (Py_ssize_t i = 0; i < len; ++i) {
-        Py_UCS4 ch = PyUnicode_READ(kind, data, i);
-
-        if (ch < 127) {
-            out[i] = (Py_UCS1)ch;
-        }
-        else if (Py_UNICODE_ISSPACE(ch)) {
-            out[i] = ' ';
-        }
-        else {
-            int decimal = Py_UNICODE_TODECIMAL(ch);
-
-            if (decimal < 0) {
-                out[i] = '?';
-                out[i + 1] = '\0';
-                break;
-            }
-            assert(decimal < 127);
-            out[i] = '0' + (Py_UCS1)decimal;
-        }
-    }
-    return result;
-}
diff --git a/utils.h b/utils.h
index 3233593f..78ee1a1d 100644
--- a/utils.h
+++ b/utils.h
@@ -34,6 +34,4 @@ int gmp_parse_pyargs(const gmp_pyargs *fnargs, Py_ssize_t argidx[],
                      PyObject *const *args, Py_ssize_t nargs,
                      PyObject *kwnames);
 
-PyObject * gmp_PyUnicode_TransformDecimalAndSpaceToASCII(PyObject *unicode);
-
 #endif /* UTILS_H */