diff --git a/Lib/test/test_builtin.py b/Lib/test/test_builtin.py
--- a/Lib/test/test_builtin.py
+++ b/Lib/test/test_builtin.py
@@ -1473,16 +1473,20 @@ class BuiltinTest(unittest.TestCase):
             for fmt_str in fmt_strs:
                 test_deprecated_format_string(cls(), fmt_str, len(fmt_str) != 0)
         # --------------------------------------------------------------------
 
         # make sure we can take a subclass of str as a format spec
         class DerivedFromStr(str): pass
         self.assertEqual(format(0, DerivedFromStr('10')), '         0')
 
+        for fmt in ['{:a}', '{:b}', '{:c}', '{:s}', '{:d}']:
+            with self.subTest(format_spec=fmt):
+                self.assertRaises(ValueError, format, b'spam', fmt)
+
     def test_bin(self):
         self.assertEqual(bin(0), '0b0')
         self.assertEqual(bin(1), '0b1')
         self.assertEqual(bin(-1), '-0b1')
         self.assertEqual(bin(2**65), '0b1' + '0' * 65)
         self.assertEqual(bin(2**65-1), '0b' + '1' * 65)
         self.assertEqual(bin(-(2**65)), '-0b1' + '0' * 65)
         self.assertEqual(bin(-(2**65-1)), '-0b' + '1' * 65)
diff --git a/Lib/test/test_format.py b/Lib/test/test_format.py
--- a/Lib/test/test_format.py
+++ b/Lib/test/test_format.py
@@ -469,11 +469,25 @@ class FormatTest(unittest.TestCase):
         f = 1.2
         with self.assertRaises(ValueError) as cm:
             format(f, ".%sf" % (INT_MAX + 1))
 
         c = complex(f)
         with self.assertRaises(ValueError) as cm:
             format(c, ".%sf" % (INT_MAX + 1))
 
+    def test_reject_formatting_on_bytes(self):
+        msg = "Unknown format code '{}' for object of type 'bytes'"
+        tests = [
+            ('{:a}', 'a'),
+            ('{:b}', 'b'),
+            ('{:c}', 'c'),
+            ('{:s}', 's'),
+            ('{:d}', 'd'),
+        ]
+        for fmt, fmt_code in tests:
+            with self.subTest(format_spec=fmt):
+                with self.assertRaises(ValueError) as cm:
+                    fmt.format(b'spam')
+                self.assertEqual(str(cm.exception), msg.format(fmt_code))
 
 if __name__ == "__main__":
     unittest.main()
diff --git a/Objects/typeobject.c b/Objects/typeobject.c
--- a/Objects/typeobject.c
+++ b/Objects/typeobject.c
@@ -4401,16 +4401,23 @@ object_format(PyObject *self, PyObject *
 {
     PyObject *format_spec;
     PyObject *self_as_str = NULL;
     PyObject *result = NULL;
 
     if (!PyArg_ParseTuple(args, "U:__format__", &format_spec))
         return NULL;
 
+    if (PyBytes_Check(self)) {
+        PyErr_Format(PyExc_ValueError,
+                     "Unknown format code %R for object of type 'bytes'",
+                     format_spec);
+        return result;
+    }
+
     self_as_str = PyObject_Str(self);
     if (self_as_str != NULL) {
         /* Issue 7994: If we're converting to a string, we
            should reject format specifications */
         if (PyUnicode_GET_LENGTH(format_spec) > 0) {
             PyErr_SetString(PyExc_TypeError,
                "non-empty format string passed to object.__format__");
             goto done;