diff --git a/Lib/test/multibytecodec_support.py b/Lib/test/multibytecodec_support.py

index f9884c6..98feec2 100644

--- a/Lib/test/multibytecodec_support.py

+++ b/Lib/test/multibytecodec_support.py

@@ -300,29 +300,23 @@ class TestBase_Mapping(unittest.TestCase):

             self._test_mapping_file_plain()

     def _test_mapping_file_plain(self):

-        unichrs = lambda s: ''.join(map(chr, map(eval, s.split('+'))))

+        def unichrs(s):

+            return ''.join(chr(int(x, 16)) for x in s.split('+'))

+

         urt_wa = {}

         with self.open_mapping_file() as f:

             for line in f:

                 if not line:

                     break

-                data = line.split('#')[0].strip().split()

+                data = line.split('#')[0].split()

                 if len(data) != 2:

                     continue

-                csetval = eval(data[0])

-                if csetval <= 0x7F:

-                    csetch = bytes([csetval & 0xff])

-                elif csetval >= 0x1000000:

-                    csetch = bytes([(csetval >> 24), ((csetval >> 16) & 0xff),

-                                    ((csetval >> 8) & 0xff), (csetval & 0xff)])

-                elif csetval >= 0x10000:

-                    csetch = bytes([(csetval >> 16), ((csetval >> 8) & 0xff),

-                                    (csetval & 0xff)])

-                elif csetval >= 0x100:

-                    csetch = bytes([(csetval >> 8), (csetval & 0xff)])

-                else:

+                if data[0][:2] != '0x':

+                    self.fail(f"Invalid line: {line!r}")

+                csetch = bytes.fromhex(data[0][2:])

+                if len(csetch) == 1 and 0x80 <= csetch[0]:

                     continue

                 unich = unichrs(data[1])