diff --git a/ext/hbsdctl.rb/glue.c b/ext/hbsdctl.rb/glue.c
index 7a367b3..b5ebc4c 100644
--- a/ext/hbsdctl.rb/glue.c
+++ b/ext/hbsdctl.rb/glue.c
@@ -8,6 +8,7 @@ int
 bsdcontrol_open(VALUE path)
 {
   int fd;
+  Check_Type(path, T_STRING);
   fd = open(RSTRING_PTR(path), O_PATH);
   if (fd == -1)
   {