diff -r f4adc2926bf5 Lib/ctypes/test/test_as_parameter.py
--- a/Lib/ctypes/test/test_as_parameter.py	Tue Apr 12 09:06:01 2011 -0700
+++ b/Lib/ctypes/test/test_as_parameter.py	Tue Apr 12 11:41:42 2011 -0700
@@ -13,6 +13,11 @@
 class POINT(Structure):
     _fields_ = [("x", c_int), ("y", c_int)]
 
+class SEVEN(Structure):
+    _fields_ = []
+    for name in ('a', 'b', 'c', 'd', 'e', 'f', 'g'):
+        _fields_.append((name, c_uint))
+
 class BasicWrapTestCase(unittest.TestCase):
     def wrap(self, param):
         return param
@@ -160,6 +165,23 @@
         expected = 203, 101, 102
         self.assertEqual(got, expected)
 
+    def test_byval_vii(self):
+        # without prototype
+        s1 = SEVEN(1, 2, 3, 4, 5, 6, 7)
+        s2 = SEVEN(0, 9, 8, 7, 6, 5, 4)
+        # EXPORT int _testfunc_byval_vii(seven s1, seven s2, unsigned int x)
+        result = dll._testfunc_byval_vii(s1, s2, 42)
+        expected = 42
+        for name, typ in SEVEN._fields_:
+            expected += getattr(s1, name) * getattr(s2, name)
+        self.assertEqual(result, expected)
+
+        # with prototype
+        dll._testfunc_byval_vii.argtypes = (SEVEN, SEVEN, c_uint)
+        dll._testfunc_byval_vii.restype = c_uint
+        result = dll._testfunc_byval_vii(s1, s2, 42)
+        self.assertEqual(result, expected)
+
     def test_struct_return_2H(self):
         class S2H(Structure):
             _fields_ = [("x", c_short),
diff -r f4adc2926bf5 Modules/_ctypes/_ctypes_test.c
--- a/Modules/_ctypes/_ctypes_test.c	Tue Apr 12 09:06:01 2011 -0700
+++ b/Modules/_ctypes/_ctypes_test.c	Tue Apr 12 11:41:42 2011 -0700
@@ -304,6 +304,28 @@
     return in.x + in.y;
 }
 
+typedef struct tagseven {
+    unsigned int a; 
+    unsigned int b;
+    unsigned int c;
+    unsigned int d;
+    unsigned int e;
+    unsigned int f;
+    unsigned int g;
+} seven;
+
+EXPORT(unsigned int) _testfunc_byval_vii(seven s1, seven s2, unsigned int x)
+{
+    return (s1.a * s2.a +
+            s1.b * s2.b +
+            s1.c * s2.c +
+            s1.d * s2.d +
+            s1.e * s2.e +
+            s1.f * s2.f +
+            s1.g * s2.g +
+            x);
+}
+
 EXPORT (int) an_integer = 42;
 
 EXPORT(int) get_an_integer(void)