diff -r 98b0ae585f5e Lib/ctypes/test/test_bitfields.py
--- a/Lib/ctypes/test/test_bitfields.py	Thu Jun 21 16:22:15 2012 +0200
+++ b/Lib/ctypes/test/test_bitfields.py	Thu Jun 21 18:19:43 2012 +0100
@@ -231,6 +231,22 @@
         else:
             self.assertEqual(sizeof(X), sizeof(c_int) * 2)
 
+    def test_sane_offsets_with_mixed_types(self):
+        class X(Structure):
+            _fields_ = [("a", c_short, 2),
+                        ("b", c_byte, 7),
+                        ("c", c_int, 28),
+                        ("d", c_short, 4)]
+
+        # Sanity checks: offsets should be such that the field
+        # fits in the containing type.
+        for name, c_type, requested_width in X._fields_:
+            field = getattr(X, name)
+            width, offset = divmod(field.size, 65536)
+            self.assertEqual(width, requested_width)
+            self.assertLessEqual(0, offset)
+            self.assertLessEqual(offset + width, sizeof(c_type) * 8)
+
     def test_anon_bitfields(self):
         # anonymous bit-fields gave a strange error message
         class X(Structure):
diff -r 98b0ae585f5e Modules/_ctypes/cfield.c
--- a/Modules/_ctypes/cfield.c	Thu Jun 21 16:22:15 2012 +0200
+++ b/Modules/_ctypes/cfield.c	Thu Jun 21 18:19:43 2012 +0100
@@ -55,6 +55,7 @@
     GETFUNC getfunc = NULL;
     StgDictObject *dict;
     int fieldtype;
+    int bit_offset;
 #define NO_BITFIELD 0
 #define NEW_BITFIELD 1
 #define CONT_BITFIELD 2
@@ -187,12 +188,22 @@
         break;
 
     case CONT_BITFIELD:
+        /* Adjust current bit offset if necessary so that the next field
+           doesn't straddle a multiple of 8*dict->size. */
+        if (*pbitofs && (
+                (*pbitofs + bitsize - 1) % (8*dict->size) !=
+                bitsize + (*pbitofs - 1) % (8*dict->size)))
+            *pbitofs += (8*dict->size) - 1 - (*pbitofs - 1) % (8*dict->size);
+
+        /* bit offset within outer field */
+        bit_offset = *pbitofs % (8*dict->size);
         if (big_endian)
-            self->size = (bitsize << 16) + *pfield_size - *pbitofs - bitsize;
+            self->size = (bitsize << 16) + *pfield_size - bit_offset - bitsize;
         else
-            self->size = (bitsize << 16) + *pbitofs;
+            self->size = (bitsize << 16) + bit_offset;
 
-        self->offset = *poffset - size; /* poffset is already updated for the NEXT field */
+        /* poffset is already updated for the NEXT field */
+        self->offset = *poffset - *pfield_size/8 + (*pbitofs - bit_offset)/8;
         *pbitofs += bitsize;
         break;
     }