diff --git a/syscall_filter.c b/syscall_filter.c
index e42f017..34f6b3a 100644
--- a/syscall_filter.c
+++ b/syscall_filter.c
@@ -33,6 +33,8 @@
 		return NE;
 	} else if (!strcmp(op_str, "&")) {
 		return SET;
+	} else if (!strcmp(op_str, "in")) {
+		return IN;
 	} else {
 		return 0;
 	}