diff --git a/src/c_client.py b/src/c_client.py
index 0213d01..6fc945f 100644
--- a/src/c_client.py
+++ b/src/c_client.py
@@ -288,7 +288,6 @@ def c_open(self):
     _c('#include "%s.h"', _ns.header)
 
     _c('')
-    _c('#define ALIGNOF(type) offsetof(struct { char dummy; type member; }, member)')
 
     if _ns.is_ext:
         for (n, h) in self.direct_imports:
@@ -1266,7 +1265,7 @@ def _c_serialize_helper_fields(context, self,
             count += 1
 
         code_lines.append(
-            '%s    xcb_align_to = ALIGNOF(%s);'
+            '%s    xcb_align_to = _Alignof(%s);'
              % (space,
                  'char'
                   if field.c_field_type == 'void' or field.type.is_switch