diff --git a/Lib/test/test_itertools.py b/Lib/test/test_itertools.py
--- a/Lib/test/test_itertools.py
+++ b/Lib/test/test_itertools.py
@@ -9,6 +9,7 @@
 import random
 import copy
 import pickle
+import struct
 from functools import reduce
 maxsize = support.MAX_Py_ssize_t
 minsize = -maxsize-1
@@ -1267,6 +1268,30 @@
         self.pickletest(a, compare=ans)
         self.pickletest(b, compare=ans)
 
+    def test_tee_sizeof(self):
+        a, b = tee(range(10000))
+        orig_size = sys.getsizeof(a)
+        self.assertEqual(sys.getsizeof(b), orig_size)
+        # When consuming a, a doesnt change size but b grows
+        take(1000, a)
+        self.assertEqual(sys.getsizeof(a), orig_size)
+        self.assertGreater(sys.getsizeof(b), orig_size)
+        size_b = sys.getsizeof(b)
+        # Again
+        take(1000, a)
+        self.assertEqual(sys.getsizeof(a), orig_size)
+        self.assertGreater(sys.getsizeof(b), size_b)
+        # Exhaust a
+        list(a)
+        self.assertEqual(sys.getsizeof(a), orig_size)
+        # 'b' holds all objects, so at least 10000 pointers + overhead
+        self.assertGreater(sys.getsizeof(b) - orig_size,
+                           10000 * struct.calcsize('P'))
+        # Exhausting b returns it to its original size, and a doesn't care
+        list(b)
+        self.assertEqual(sys.getsizeof(b), orig_size)
+        self.assertEqual(sys.getsizeof(a), orig_size)
+
     # Issue 13454: Crash when deleting backward iterator from tee()
     def test_tee_del_backward(self):
         forward, backward = tee(repeat(None, 20000000))
diff --git a/Modules/itertoolsmodule.c b/Modules/itertoolsmodule.c
--- a/Modules/itertoolsmodule.c
+++ b/Modules/itertoolsmodule.c
@@ -755,12 +755,29 @@
     Py_RETURN_NONE;
 }
 
+PyDoc_STRVAR(sizeof_doc,
+"Return the memory size of the object in bytes");
+
+static PyObject *
+tee_sizeof(teeobject *to, void *unused)
+{
+    Py_ssize_t size = sizeof(teeobject);
+    teedataobject *tdo = to->dataobj;
+    while (tdo != NULL) {
+        assert(Py_TYPE(tdo) == &teedataobject_type);
+        size += sizeof(teedataobject);
+        tdo = (teedataobject *) tdo->nextlink;
+    }
+    return PyLong_FromSsize_t(size);
+}
+
 PyDoc_STRVAR(teeobject_doc,
 "Iterator wrapped to make it copyable");
 
 static PyMethodDef tee_methods[] = {
     {"__copy__",        (PyCFunction)tee_copy,  METH_NOARGS, teecopy_doc},
     {"__reduce__",      (PyCFunction)tee_reduce,      METH_NOARGS, reduce_doc},
+    {"__sizeof__",      (PyCFunction)tee_sizeof, METH_NOARGS, sizeof_doc},
     {"__setstate__",    (PyCFunction)tee_setstate,    METH_O, setstate_doc},
     {NULL,              NULL}           /* sentinel */
 };