diff --git a/Lib/test/test_capi.py b/Lib/test/test_capi.py
--- a/Lib/test/test_capi.py
+++ b/Lib/test/test_capi.py
@@ -90,6 +90,14 @@
                 return 1
         self.assertRaises(TypeError, _posixsubprocess.fork_exec,
                           1,Z(),3,[1, 2],5,6,7,8,9,10,11,12,13,14,15,16,17)
+        # Issue #XYZ: overflow in _PySequence_BytesToCharpArray()
+        class Z(object):
+            def __len__(self):
+                return sys.maxsize
+            def __getitem__(self, i):
+                return b'x'
+        self.assertRaises(MemoryError, _posixsubprocess.fork_exec,
+                          1,Z(),3,[1, 2],5,6,7,8,9,10,11,12,13,14,15,16,17)
 
 @unittest.skipUnless(threading, 'Threading required for this test.')
 class TestPendingCalls(unittest.TestCase):
diff --git a/Objects/abstract.c b/Objects/abstract.c
--- a/Objects/abstract.c
+++ b/Objects/abstract.c
@@ -2710,6 +2710,11 @@
     if (argc == -1)
         return NULL;
 
+    if (argc > (PY_SSIZE_T_MAX-sizeof(char *)) / sizeof(char *)) {
+        PyErr_NoMemory();
+        return NULL;
+    }
+
     array = malloc((argc + 1) * sizeof(char *));
     if (array == NULL) {
         PyErr_NoMemory();