diff --git a/Lib/test/test_io.py b/Lib/test/test_io.py
index caca0333e0d82f..3dc6e9ffcac157 100644
--- a/Lib/test/test_io.py
+++ b/Lib/test/test_io.py
@@ -2702,6 +2702,26 @@ def _make_illegal_wrapper():
             #t = _make_illegal_wrapper()
             #self.assertRaises(TypeError, t.read)
 
+        # Issue 31243: calling read() while the return value of decoder's
+        # getstate() is invalid should neither crash the interpreter nor
+        # raise a SystemError.
+        def _make_very_illegal_wrapper(getstate_ret_val):
+            class BadDecoder:
+                def getstate(self):
+                    return getstate_ret_val
+            def _get_bad_decoder(dummy):
+                return BadDecoder()
+            quopri = codecs.lookup("quopri_codec")
+            with support.swap_attr(quopri, 'incrementaldecoder',
+                                   _get_bad_decoder):
+                return _make_illegal_wrapper()
+        t = _make_very_illegal_wrapper(42)
+        with self.maybeRaises(TypeError):
+            t.read(42)
+        t = _make_very_illegal_wrapper(())
+        with self.maybeRaises(TypeError):
+            t.read(42)
+
 
 class CTextIOWrapperTest(TextIOWrapperTest):
 
diff --git a/Misc/NEWS.d/next/Core and Builtins/2017-08-29-14-24-34.bpo-31243.tr0E4V.rst b/Misc/NEWS.d/next/Core and Builtins/2017-08-29-14-24-34.bpo-31243.tr0E4V.rst
new file mode 100644
index 00000000000000..166458f2b785ab
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2017-08-29-14-24-34.bpo-31243.tr0E4V.rst	
@@ -0,0 +1,2 @@
+Fix a crash in some methods of `io.TextIOWrapper`, when the decoder's state
+is invalid. Patch by Oren Milman.
diff --git a/Modules/_io/textio.c b/Modules/_io/textio.c
index f13dcb4366e06f..d9e036db386d3b 100644
--- a/Modules/_io/textio.c
+++ b/Modules/_io/textio.c
@@ -1416,7 +1416,7 @@ textiowrapper_read_chunk(textio *self)
         /* Given this, we know there was a valid snapshot point
          * len(dec_buffer) bytes ago with decoder state (b'', dec_flags).
          */
-        if (PyArg_Parse(state, "(OO)", &dec_buffer, &dec_flags) < 0) {
+        if (!PyArg_Parse(state, "(OO)", &dec_buffer, &dec_flags)) {
             Py_DECREF(state);
             return -1;
         }
diff --git a/Modules/_testcapimodule.c b/Modules/_testcapimodule.c
index a5e3f07667d07a..ecc473cf4c1521 100644
--- a/Modules/_testcapimodule.c
+++ b/Modules/_testcapimodule.c
@@ -911,8 +911,9 @@ test_L_code(PyObject *self)
     PyTuple_SET_ITEM(tuple, 0, num);
 
     value = -1;
-    if (PyArg_ParseTuple(tuple, "L:test_L_code", &value) < 0)
+    if (!PyArg_ParseTuple(tuple, "L:test_L_code", &value)) {
         return NULL;
+    }
     if (value != 42)
         return raiseTestError("test_L_code",
             "L code returned wrong value for long 42");
@@ -925,8 +926,9 @@ test_L_code(PyObject *self)
     PyTuple_SET_ITEM(tuple, 0, num);
 
     value = -1;
-    if (PyArg_ParseTuple(tuple, "L:test_L_code", &value) < 0)
+    if (!PyArg_ParseTuple(tuple, "L:test_L_code", &value)) {
         return NULL;
+    }
     if (value != 42)
         return raiseTestError("test_L_code",
             "L code returned wrong value for int 42");
@@ -1207,8 +1209,9 @@ test_k_code(PyObject *self)
     PyTuple_SET_ITEM(tuple, 0, num);
 
     value = 0;
-    if (PyArg_ParseTuple(tuple, "k:test_k_code", &value) < 0)
+    if (!PyArg_ParseTuple(tuple, "k:test_k_code", &value)) {
         return NULL;
+    }
     if (value != ULONG_MAX)
         return raiseTestError("test_k_code",
             "k code returned wrong value for long 0xFFF...FFF");
@@ -1226,8 +1229,9 @@ test_k_code(PyObject *self)
     PyTuple_SET_ITEM(tuple, 0, num);
 
     value = 0;
-    if (PyArg_ParseTuple(tuple, "k:test_k_code", &value) < 0)
+    if (!PyArg_ParseTuple(tuple, "k:test_k_code", &value)) {
         return NULL;
+    }
     if (value != (unsigned long)-0x42)
         return raiseTestError("test_k_code",
             "k code returned wrong value for long -0xFFF..000042");
@@ -1587,14 +1591,16 @@ test_u_code(PyObject *self)
     PyTuple_SET_ITEM(tuple, 0, obj);
 
     value = 0;
-    if (PyArg_ParseTuple(tuple, "u:test_u_code", &value) < 0)
+    if (!PyArg_ParseTuple(tuple, "u:test_u_code", &value)) {
         return NULL;
+    }
     if (value != PyUnicode_AS_UNICODE(obj))
         return raiseTestError("test_u_code",
             "u code returned wrong value for u'test'");
     value = 0;
-    if (PyArg_ParseTuple(tuple, "u#:test_u_code", &value, &len) < 0)
+    if (!PyArg_ParseTuple(tuple, "u#:test_u_code", &value, &len)) {
         return NULL;
+    }
     if (value != PyUnicode_AS_UNICODE(obj) ||
         len != PyUnicode_GET_SIZE(obj))
         return raiseTestError("test_u_code",
@@ -1692,8 +1698,9 @@ test_empty_argparse(PyObject *self)
     tuple = PyTuple_New(0);
     if (!tuple)
         return NULL;
-    if ((result = PyArg_ParseTuple(tuple, "|:test_empty_argparse")) < 0)
+    if (!(result = PyArg_ParseTuple(tuple, "|:test_empty_argparse"))) {
         goto done;
+    }
     dict = PyDict_New();
     if (!dict)
         goto done;
@@ -1701,8 +1708,9 @@ test_empty_argparse(PyObject *self)
   done:
     Py_DECREF(tuple);
     Py_XDECREF(dict);
-    if (result < 0)
+    if (!result) {
         return NULL;
+    }
     else {
         Py_RETURN_NONE;
     }
@@ -2494,8 +2502,9 @@ test_raise_signal(PyObject* self, PyObject *args)
 {
     int signum, err;
 
-    if (PyArg_ParseTuple(args, "i:raise_signal", &signum) < 0)
+    if (!PyArg_ParseTuple(args, "i:raise_signal", &signum)) {
         return NULL;
+    }
 
     err = raise(signum);
     if (err)