diff --git a/drivers/firmware/efi/cper.c b/drivers/firmware/efi/cper.c
index 7f89a9fb2eca..16b27fe9608f 100644
--- a/drivers/firmware/efi/cper.c
+++ b/drivers/firmware/efi/cper.c
@@ -162,7 +162,7 @@ int cper_bits_to_str(char *buf, int buf_size, unsigned long bits,
 		len -= size;
 		str += size;
 	}
-	return len - buf_size;
+	return buf_size - len;
 }
 EXPORT_SYMBOL_GPL(cper_bits_to_str);