diff --git a/libratbox/src/linebuf.c b/libratbox/src/linebuf.c
index 32d09a60..c5472dfc 100644
--- a/libratbox/src/linebuf.c
+++ b/libratbox/src/linebuf.c
@@ -446,6 +446,8 @@ rb_linebuf_get(rb_buf_head_t * bufhead, char *buf, size_t buflen, bool partial,
 	size_t cpylen;
 	char *start, *ch;
 
+	lrb_assert(buflen > 0);
+
 	/* make sure we have a line */
 	if(bufhead->list.head == NULL)
 		return 0;	/* Obviously not.. hrm. */
@@ -897,4 +899,3 @@ unsigned int rb_linebuf_numlines(rb_buf_head_t *bufhead)
 {
 	return bufhead->numlines;
 }
-