Index: Modules/structmodule.c
===================================================================
--- Modules/structmodule.c	(Revision 42524)
+++ Modules/structmodule.c	(Arbeitskopie)
@@ -120,16 +120,22 @@
 static int
 get_ulong(PyObject *v, unsigned long *p)
 {
+	int result;
 	if (PyLong_Check(v)) {
 		unsigned long x = PyLong_AsUnsignedLong(v);
 		if (x == (unsigned long)(-1) && PyErr_Occurred())
 			return -1;
 		*p = x;
 		return 0;
+	} else {
+		result = get_long(v, (long *)p);
+		if ((result == 0) && ((long)*p < 0)) {
+			PyErr_SetString(StructError,
+					"unsigned long argument must be positive");
+			return -1;
+		}
+		return result;
 	}
-	else {
-		return get_long(v, (long *)p);
-	}
 }
 
 #ifdef HAVE_LONG_LONG