diff --git a/extlib/benz/include/picrin/util.h b/extlib/benz/include/picrin/util.h
index 5c831bad..ad816c70 100644
--- a/extlib/benz/include/picrin/util.h
+++ b/extlib/benz/include/picrin/util.h
@@ -56,11 +56,19 @@ extern "C" {
 # define PIC_GENSYM(x) PIC_GENSYM1_(__LINE__,x)
 #endif
 
+#if __GNUC__
+# define GCC_VERSION (__GNUC__ * 10000          \
+   + __GNUC_MINOR__ * 100                       \
+   + __GNUC_PATCHLEVEL__)
+#endif
 #if GCC_VERSION >= 40500 || __clang__
 # define PIC_UNREACHABLE() (__builtin_unreachable())
 #else
 # define PIC_UNREACHABLE() (assert(false))
 #endif
+#if __GNUC__
+# undef GCC_VERSION
+#endif
 
 #define PIC_SWAP(type,a,b)                      \
   PIC_SWAP_HELPER_(type, PIC_GENSYM(tmp), a, b)