diff -r 0b04e5689c33 Lib/test/test_capi.py
--- a/Lib/test/test_capi.py	Wed Jul 15 22:12:33 2015 +0300
+++ b/Lib/test/test_capi.py	Wed Jul 15 18:22:56 2015 -0400
@@ -477,7 +477,8 @@
             # skip parentheses, the error reporting is inconsistent about them
             # skip 'e', it's always a two-character code
             # skip '|' and '$', they don't represent arguments anyway
-            if c in '()e|$':
+            # skip 'w' because it is invalid without a suffix.
+            if c in 'w()e|$':
                 continue
 
             # test the format unit when not skipped
diff -r 0b04e5689c33 Misc/NEWS
--- a/Misc/NEWS	Wed Jul 15 22:12:33 2015 +0300
+++ b/Misc/NEWS	Wed Jul 15 18:22:56 2015 -0400
@@ -32,6 +32,9 @@
 Core and Builtins
 -----------------
 
+- Issue: #23926: Fixed skipitem()'s handling of the old 'w' and 'w#' formatters.
+  These are no longer supported and now raise an exception if used.
+
 - Issue #24569: Make PEP 448 dictionary evaluation more consistent.
 
 - Issue #24407: Fix crash when dict is mutated while being updated.
diff -r 0b04e5689c33 Modules/_testcapimodule.c
--- a/Modules/_testcapimodule.c	Wed Jul 15 22:12:33 2015 +0300
+++ b/Modules/_testcapimodule.c	Wed Jul 15 18:22:56 2015 -0400
@@ -1443,6 +1443,77 @@
     Py_RETURN_NONE;
 }
 
+/* Test the old w and w# codes that no longer work */
+static PyObject *
+test_w_code_invalid(PyObject *self)
+{
+    static const char * const keywords[] = {"a", "b", "c", "d", NULL};
+    char *formats_3[] = {"O|w#$O",
+                         "O|w$O",
+                         "O|w#O",
+                         "O|wO",
+                         NULL};
+    char *formats_4[] = {"O|w#O$O",
+                         "O|wO$O",
+                         "O|Ow#O",
+                         "O|OwO",
+                         "O|Ow#$O",
+                         "O|Ow$O",
+                         NULL};
+    size_t n;
+    PyObject *args;
+    PyObject *kwargs;
+    PyObject *tmp;
+
+    if (!(args = PyTuple_Pack(1, Py_None))) {
+        return NULL;
+    }
+
+    if (!(kwargs = PyDict_New()) || PyDict_SetItemString(kwargs, "c", Py_None)) {
+        Py_DECREF(args);
+        Py_XDECREF(kwargs);
+        return NULL;
+    }
+
+    for (n = 0;formats_3[n];++n) {
+        if (PyArg_ParseTupleAndKeywords(args, kwargs, formats_3[n],
+                                        (char**) keywords,
+                                        &tmp, &tmp, &tmp)) {
+            Py_DECREF(args);
+            return raiseTestError("test_w_code_invalid_suffix",
+                                  formats_3[n]);
+        }
+        else {
+            PyErr_Clear();
+        }
+    }
+
+    if (PyDict_DelItemString(kwargs, "c") ||
+        PyDict_SetItemString(kwargs, "d", Py_None)) {
+
+        Py_DECREF(kwargs);
+        Py_DECREF(args);
+        return NULL;
+    }
+
+    for (n = 0;formats_4[n];++n) {
+        if (PyArg_ParseTupleAndKeywords(args, kwargs, formats_4[n],
+                                        (char**) keywords,
+                                        &tmp, &tmp, &tmp, &tmp)) {
+            Py_DECREF(args);
+            return raiseTestError("test_w_code_invalid_suffix",
+                                  formats_4[n]);
+        }
+        else {
+            PyErr_Clear();
+        }
+    }
+
+    Py_DECREF(args);
+    Py_DECREF(kwargs);
+    Py_RETURN_NONE;
+}
+
 static PyObject *
 test_widechar(PyObject *self)
 {
@@ -3600,6 +3671,7 @@
     {"test_s_code",             (PyCFunction)test_s_code,        METH_NOARGS},
     {"test_u_code",             (PyCFunction)test_u_code,        METH_NOARGS},
     {"test_Z_code",             (PyCFunction)test_Z_code,        METH_NOARGS},
+    {"test_w_code_invalid",     (PyCFunction)test_w_code_invalid,METH_NOARGS},
     {"test_widechar",           (PyCFunction)test_widechar,      METH_NOARGS},
     {"unicode_aswidechar",      unicode_aswidechar,              METH_VARARGS},
     {"unicode_aswidecharstring",unicode_aswidecharstring,        METH_VARARGS},
diff -r 0b04e5689c33 Python/getargs.c
--- a/Python/getargs.c	Wed Jul 15 22:12:33 2015 +0300
+++ b/Python/getargs.c	Wed Jul 15 18:22:56 2015 -0400
@@ -1671,6 +1671,14 @@
 
     /* string codes */
 
+    case 'w': /* buffer, read-write */
+        if (*format != '*') {
+            /* after 'w', only '*' is allowed */
+            goto err;
+        }
+        format++;
+        break;
+
     case 'e': /* string with encoding */
         {
             (void) va_arg(*p_va, const char *);
@@ -1686,7 +1694,6 @@
     case 'y': /* bytes */
     case 'u': /* unicode string */
     case 'Z': /* unicode string or None */
-    case 'w': /* buffer, read-write */
         {
             (void) va_arg(*p_va, char **);
             if (*format == '#') {