diff --git a/rdesktop.c b/rdesktop.c
index ce4acdc..4148140 100644
--- a/rdesktop.c
+++ b/rdesktop.c
@@ -1790,7 +1790,7 @@ str_handle_lines(const char *input, char **rest, str_handle_lines_t linehandler,
 	buf[0] = '\0';
 	if (*rest)
 		STRNCPY(buf, *rest, buflen);
-	strncat(buf, input, inputlen);
+	strncat(buf, input, buflen);
 	p = buf;
 
 	while (1)