diff --git a/filter/filter.c b/filter/filter.c
index 98c657b0..b3b17dcf 100644
--- a/filter/filter.c
+++ b/filter/filter.c
@@ -1214,6 +1214,7 @@ i_same(struct f_inst *f1, struct f_inst *f2)
   case '|':
   case '&':
   case P('m','p'):
+  case P('m','c'):
   case P('!','='):
   case P('=','='):
   case '<':