diff --git a/src/input/rs232.c b/src/input/rs232.c
index 2fd2a09..9da01a3 100644
--- a/src/input/rs232.c
+++ b/src/input/rs232.c
@@ -270,7 +270,7 @@
 	if (rc < 0) {
 		close(bfd->fd);
 		LOGP(DLMI, LOGL_ERROR, "rs232: could not register FD: %s\n",
-			strerror(rc));
+			strerror(-rc));
 		return rc;
 	}