diff --git a/src/importc.h b/src/importc.h
index a15ceb8058..7156c11fb7 100644
--- a/src/importc.h
+++ b/src/importc.h
@@ -55,3 +55,13 @@
  * Define it to do what other C compilers do.
  */
 #define __builtin_offsetof(t,i) ((typeof(sizeof(0)))((char *)&((t *)0)->i - (char *)0))
+
+/****************************
+ * Define it to do what other C compilers do.
+ */
+#define _Alignof(type) __builtin_offsetof(struct { char c; type member; }, member)
+
+/****************************
+ * clang's preprocessor generates __alignof instead
+ */
+#define __alignof _Alignof