diff --git a/Lib/test/test_base64.py b/Lib/test/test_base64.py
--- a/Lib/test/test_base64.py
+++ b/Lib/test/test_base64.py
@@ -22,6 +22,8 @@
            b"YWJjZGVmZ2hpamtsbW5vcHFyc3R1dnd4eXpBQkNE"
            b"RUZHSElKS0xNTk9QUVJTVFVWV1hZWjAxMjM0\nNT"
            b"Y3ODkhQCMwXiYqKCk7Ojw+LC4gW117fQ==\n")
+        # Test for bytearray, issue17842
+        eq(base64.encodebytes(bytearray(b'abcd')), b'YWJjZA==\n')
         self.assertRaises(TypeError, base64.encodebytes, "")
 
     def test_decodebytes(self):
@@ -76,6 +78,8 @@
            b"YWJjZGVmZ2hpamtsbW5vcHFyc3R1dnd4eXpBQkNE"
            b"RUZHSElKS0xNTk9QUVJTVFVWV1hZWjAxMjM0NT"
            b"Y3ODkhQCMwXiYqKCk7Ojw+LC4gW117fQ==")
+        # Test for bytearray, issue17842
+        eq(base64.b64encode(bytearray(b'abcd')), b'YWJjZA==')
         # Test with arbitrary alternative characters
         eq(base64.b64encode(b'\xd3V\xbeo\xf7\x1d', altchars=b'*$'), b'01a*b$cd')
         # Check if passing a str object raises an error
@@ -93,6 +97,8 @@
            b"YWJjZGVmZ2hpamtsbW5vcHFyc3R1dnd4eXpBQkNE"
            b"RUZHSElKS0xNTk9QUVJTVFVWV1hZWjAxMjM0NT"
            b"Y3ODkhQCMwXiYqKCk7Ojw+LC4gW117fQ==")
+        # Test for bytearray, issue17842
+        eq(base64.standard_b64encode(bytearray(b'abcd')), b'YWJjZA==')
         # Check if passing a str object raises an error
         self.assertRaises(TypeError, base64.standard_b64encode, "")
         self.assertRaises(TypeError, base64.standard_b64encode, b"", altchars="")
@@ -179,6 +185,8 @@
         eq(base64.b32encode(b'abc'), b'MFRGG===')
         eq(base64.b32encode(b'abcd'), b'MFRGGZA=')
         eq(base64.b32encode(b'abcde'), b'MFRGGZDF')
+        # Test for bytearray, issue17842
+        eq(base64.b32encode(bytearray(b'abcd')), b'MFRGGZA=')
         self.assertRaises(TypeError, base64.b32encode, "")
 
     def test_b32decode(self):
@@ -245,6 +253,8 @@
         eq = self.assertEqual
         eq(base64.b16encode(b'\x01\x02\xab\xcd\xef'), b'0102ABCDEF')
         eq(base64.b16encode(b'\x00'), b'00')
+        # Test for bytearray, issue17842
+        eq(base64.b16encode(bytearray(b'\x01\x02\xab\xcd\xef')), b'0102ABCDEF')
         self.assertRaises(TypeError, base64.b16encode, "")
 
     def test_b16decode(self):