diff --git a/buffer/bs_seterrorstate.c b/buffer/bs_seterrorstate.c
new file mode 100644
index 0000000..ec32b2c
--- /dev/null
+++ b/buffer/bs_seterrorstate.c
@@ -0,0 +1,6 @@
+#include "parse.h"
+
+void bs_seterrorstate(struct bytestream* b) {
+  b->cur = 1;
+  b->max = 0;
+}
diff --git a/parse.h b/parse.h
index 9dbd32d..b82a44a 100644
--- a/parse.h
+++ b/parse.h
@@ -83,6 +83,9 @@ unsigned char bs_peek(struct bytestream* bs);
 /* was there a read error or did we attempt to read more than maxlen bytes? */
 int bs_err(struct bytestream* bs);
 
+/* mark bytestream as erroneous */
+void bs_seterrorstate(struct bytestream* b);
+
 /* Can we read this much more bytes from the bytestream? */
 /* returns 1 for yes, 0 for no */
 int bs_capacitycheck(struct bytestream* bs,size_t capacity);