diff -r 94628dc3b05c Lib/test/test_struct.py
--- a/Lib/test/test_struct.py	Mon Sep 30 21:50:21 2013 -0400
+++ b/Lib/test/test_struct.py	Tue Oct 01 11:51:20 2013 +0800
@@ -574,6 +574,14 @@
         self.check_sizeof('0s', 1)
         self.check_sizeof('0c', 0)
 
+    def test_ascii_range_unicode_format(self):
+        # issue 19099
+        struct._clearcache()
+        self.assertEqual(struct.pack(u'B', 1), '\x01')
+
+    def test_outside_ascii_range_unicode_format(self):
+        self.assertRaises(struct.error, struct.pack, u'\xff', 1)
+
 def test_main():
     support.run_unittest(StructTest)
 
diff -r 94628dc3b05c Modules/_struct.c
--- a/Modules/_struct.c	Mon Sep 30 21:50:21 2013 -0400
+++ b/Modules/_struct.c	Tue Oct 01 11:51:20 2013 +0800
@@ -1856,12 +1856,24 @@
 {
     PyObject *s_object, *fmt, *newargs, *result;
     Py_ssize_t n = PyTuple_GET_SIZE(args);
+    const char* s;
 
     if (n == 0) {
         PyErr_SetString(PyExc_TypeError, "missing format argument");
         return NULL;
     }
     fmt = PyTuple_GET_ITEM(args, 0);
+    /* Accept ascii-range unicode argument, e.g. struct.pack(u'b', 1) */
+    if (PyUnicode_Check(fmt)) {
+        s = PyString_AsString(fmt);
+        if (s == NULL) {
+            PyErr_SetString(StructError, "bad char in struct format");
+            return NULL;
+        } else {
+            fmt = PyString_FromString(s);
+            Py_DECREF(s);
+        }
+    }
     newargs = PyTuple_GetSlice(args, 1, n);
     if (newargs == NULL)
         return NULL;