diff --git a/py/objstr.c b/py/objstr.c
index 814dd9e132..f1e4e6b7bf 100644
--- a/py/objstr.c
+++ b/py/objstr.c
@@ -578,7 +578,7 @@ STATIC mp_obj_t str_rsplit(mp_uint_t n_args, const mp_obj_t *args) {
     mp_int_t idx = splits;
 
     if (sep == mp_const_none) {
-        assert(!"TODO: rsplit(None,n) not implemented");
+        mp_not_implemented("rsplit(None,n)");
     } else {
         mp_uint_t sep_len;
         const char *sep_str = mp_obj_str_get_data(sep, &sep_len);
diff --git a/tests/misc/non_compliant.py b/tests/misc/non_compliant.py
index ee1dcf3416..79f1e70c88 100644
--- a/tests/misc/non_compliant.py
+++ b/tests/misc/non_compliant.py
@@ -39,3 +39,9 @@ try:
     print('{a[0]}'.format(a=[1, 2]))
 except NotImplementedError:
     print('NotImplementedError')
+
+# str.rsplit(None, n) not implemented
+try:
+    'a a a'.rsplit(None, 1)
+except NotImplementedError:
+    print('NotImplementedError')
diff --git a/tests/misc/non_compliant.py.exp b/tests/misc/non_compliant.py.exp
index 731dd220b5..3790f4f346 100644
--- a/tests/misc/non_compliant.py.exp
+++ b/tests/misc/non_compliant.py.exp
@@ -4,3 +4,4 @@ True
 True
 TypeError, ValueError
 NotImplementedError
+NotImplementedError