diff --git a/openbsc/src/gsm_04_80.c b/openbsc/src/gsm_04_80.c
index 135582d..28f9b92 100644
--- a/openbsc/src/gsm_04_80.c
+++ b/openbsc/src/gsm_04_80.c
@@ -54,7 +54,7 @@
 	uint8_t *data = msgb_push(msgb, 2);
 
 	data[0] = tag;
-	data[1] = msgb->len;
+	data[1] = msgb->len - 2;
 	return data;
 }