diff --git a/build/ax_cxx_compile_stdcxx_11.m4 b/build/ax_cxx_compile_stdcxx_11.m4
index d8a1aee..fa325de 100644
--- a/build/ax_cxx_compile_stdcxx_11.m4
+++ b/build/ax_cxx_compile_stdcxx_11.m4
@@ -40,6 +40,8 @@
 # feature we need right now from C++0x
 m4_define([_AX_CXX_COMPILE_STDCXX_11_testbody], [[
     #include <unordered_map>
+    struct Foo { int x; };
+    void bar() { int y = sizeof(Foo::x); }
 ]])

 AC_DEFUN([AX_CXX_COMPILE_STDCXX_11], [dnl