diff --git a/Lib/test/test_zlib.py b/Lib/test/test_zlib.py
index 7593c06..f991900 100644
--- a/Lib/test/test_zlib.py
+++ b/Lib/test/test_zlib.py
@@ -350,6 +350,15 @@
         self.assertRaises(ValueError, dco.decompress, b"", -1)
         self.assertEqual(b'', dco.unconsumed_tail)
 
+    def test_clear_unconsumed_tail(self):
+        # Issue #12050: calling decompress() without providing max_length
+        # should clear the unconsumed_tail attribute.
+        cdata = b"x\x9cKLJ\x06\x00\x02M\x01"    # "abc"
+        dco = zlib.decompressobj()
+        ddata = dco.decompress(cdata, 1)
+        ddata += dco.decompress(dco.unconsumed_tail)
+        self.assertEqual(dco.unconsumed_tail, b"")
+
     def test_flushes(self):
         # Test flush() with the various options, using all the
         # different levels in order to provide more variations.