diff --git a/Objects/listobject.c b/Objects/listobject.c
index cea9b24a3b2fb6..d199290c99a724 100644
--- a/Objects/listobject.c
+++ b/Objects/listobject.c
@@ -291,12 +291,8 @@ ins1(PyListObject *self, Py_ssize_t where, PyObject *v)
         PyErr_BadInternalCall();
         return -1;
     }
-    if (n == PY_SSIZE_T_MAX) {
-        PyErr_SetString(PyExc_OverflowError,
-            "cannot add more objects to list");
-        return -1;
-    }
 
+    assert((size_t)n + 1 < PY_SSIZE_T_MAX);
     if (list_resize(self, n+1) < 0)
         return -1;
 
@@ -331,12 +327,7 @@ app1(PyListObject *self, PyObject *v)
     Py_ssize_t n = PyList_GET_SIZE(self);
 
     assert (v != NULL);
-    if (n == PY_SSIZE_T_MAX) {
-        PyErr_SetString(PyExc_OverflowError,
-            "cannot add more objects to list");
-        return -1;
-    }
-
+    assert((size_t)n + 1 < PY_SSIZE_T_MAX);
     if (list_resize(self, n+1) < 0)
         return -1;
 
@@ -528,8 +519,7 @@ list_concat(PyListObject *a, PyObject *bb)
         return NULL;
     }
 #define b ((PyListObject *)bb)
-    if (Py_SIZE(a) > PY_SSIZE_T_MAX - Py_SIZE(b))
-        return PyErr_NoMemory();
+    assert((size_t)Py_SIZE(a) + (size_t)Py_SIZE(b) < PY_SSIZE_T_MAX);
     size = Py_SIZE(a) + Py_SIZE(b);
     np = (PyListObject *) list_new_prealloc(size);
     if (np == NULL) {
diff --git a/Objects/tupleobject.c b/Objects/tupleobject.c
index aeaf845d74cfa1..77fb2e5393de55 100644
--- a/Objects/tupleobject.c
+++ b/Objects/tupleobject.c
@@ -483,8 +483,7 @@ tupleconcat(PyTupleObject *a, PyObject *bb)
         Py_INCREF(a);
         return (PyObject *)a;
     }
-    if (Py_SIZE(a) > PY_SSIZE_T_MAX - Py_SIZE(b))
-        return PyErr_NoMemory();
+    assert((size_t)Py_SIZE(a) + (size_t)Py_SIZE(b) < PY_SSIZE_T_MAX);
     size = Py_SIZE(a) + Py_SIZE(b);
     np = (PyTupleObject *) PyTuple_New(size);
     if (np == NULL) {