diff -r c1414f80ebc9 Include/pymacro.h
--- a/Include/pymacro.h	Thu Nov 05 13:56:58 2015 +0100
+++ b/Include/pymacro.h	Thu Nov 05 17:59:13 2015 +0100
@@ -33,8 +33,10 @@
         + Py_BUILD_ASSERT_EXPR(offsetof(struct foo, string) == 0))
 
    Written by Rusty Russell, public domain, http://ccodearchive.net/ */
+#define _Py_BUILD_ASSERT_EXPR(cond) \
+    (sizeof(char [1 - 2*!(cond)]) - 1)
 #define Py_BUILD_ASSERT_EXPR(cond) \
-    (sizeof(char [1 - 2*!(cond)]) - 1)
+    (void)_Py_BUILD_ASSERT_EXPR(cond)
 
 /* Get the number of elements in a visible array
 
@@ -51,7 +53,7 @@
    &a[0] degrades to a pointer: a different type from an array */
 #define Py_ARRAY_LENGTH(array) \
     (sizeof(array) / sizeof((array)[0]) \
-     + Py_BUILD_ASSERT_EXPR(!__builtin_types_compatible_p(typeof(array), \
+     + _Py_BUILD_ASSERT_EXPR(!__builtin_types_compatible_p(typeof(array), \
                                                           typeof(&(array)[0]))))
 #else
 #define Py_ARRAY_LENGTH(array) \