diff --git a/filter/filter.h b/filter/filter.h
index 4af93175..059636ea 100644
--- a/filter/filter.h
+++ b/filter/filter.h
@@ -106,6 +106,7 @@ void val_print(struct f_val v);
 #define T_ENUM_HI 0x3f
 
 #define T_ENUM_RTS 0x30
+#define T_ENUM_EMPTY 0x3f	/* Special hack for atomic_aggr */
 
 #define T_ENUM T_ENUM_LO ... T_ENUM_HI