diff --git a/sys/sys/tree.h b/sys/sys/tree.h
index 063b03ca95f..6682ec7762f 100644
--- a/sys/sys/tree.h
+++ b/sys/sys/tree.h
@@ -332,7 +332,7 @@ struct {								\
 } while (/*CONSTCOND*/ 0)
 
 #ifndef RB_AUGMENT
-#define RB_AUGMENT(x)
+#define RB_AUGMENT(x)	do {} while (0)
 #endif
 
 #define RB_ROTATE_LEFT(head, elm, tmp, field) do {			\