diff --git a/py/objstr.c b/py/objstr.c
index 274e76daaaeff6e98171a4562456281bc5987571..704fa07e1de54ca956f8912e7a2ff75bf397eb3e 100644
--- a/py/objstr.c
+++ b/py/objstr.c
@@ -699,7 +699,9 @@ STATIC mp_obj_t str_startswith(mp_uint_t n_args, const mp_obj_t *args) {
 STATIC mp_obj_t str_endswith(mp_uint_t n_args, const mp_obj_t *args) {
     GET_STR_DATA_LEN(args[0], str, str_len);
     GET_STR_DATA_LEN(args[1], suffix, suffix_len);
-    assert(n_args == 2);
+    if (n_args > 2) {
+        mp_not_implemented("start/end indices");
+    }
 
     if (suffix_len > str_len) {
         return mp_const_false;
diff --git a/tests/misc/non_compliant.py b/tests/misc/non_compliant.py
index 09abac238858a03800095b5ee7ca7f9a85f26004..de845790670dec6101250be7957f10e6d5957e07 100644
--- a/tests/misc/non_compliant.py
+++ b/tests/misc/non_compliant.py
@@ -52,6 +52,12 @@ try:
 except NotImplementedError:
     print('NotImplementedError')
 
+# str.endswith(s, start) not implemented
+try:
+    'abc'.endswith('c', 1)
+except NotImplementedError:
+    print('NotImplementedError')
+
 # bytes(...) with keywords not implemented
 try:
     bytes('abc', encoding='utf8')
diff --git a/tests/misc/non_compliant.py.exp b/tests/misc/non_compliant.py.exp
index 9278034aa42e104b50bef4187f2fc3f1ed56544d..28b1470d7c580ec6327a22d72e63bbfd9b04993a 100644
--- a/tests/misc/non_compliant.py.exp
+++ b/tests/misc/non_compliant.py.exp
@@ -8,3 +8,4 @@ NotImplementedError
 NotImplementedError
 NotImplementedError
 NotImplementedError
+NotImplementedError