diff --git a/buffer/bs_err.c b/buffer/bs_err.c
new file mode 100644
index 0000000..f7867b5
--- /dev/null
+++ b/buffer/bs_err.c
@@ -0,0 +1,6 @@
+#include "parse.h"
+
+int bs_err(struct bytestream* bs) {
+  return (bs->cur > bs->max);
+}
+