diff --git a/tools/lib/api/io.h b/tools/lib/api/io.h
index d3eb04d1bc897..1731996b2c32a 100644
--- a/tools/lib/api/io.h
+++ b/tools/lib/api/io.h
@@ -189,6 +189,7 @@ static inline ssize_t io__getdelim(struct io *io, char **line_out, size_t *line_
 err_out:
 	free(line);
 	*line_out = NULL;
+	*line_len_out = 0;
 	return -ENOMEM;
 }