diff --git a/backend_common.c b/backend_common.c
index 4f4a930..e5ea6e7 100644
--- a/backend_common.c
+++ b/backend_common.c
@@ -508,7 +508,7 @@ int main (int argc, char **argv)
 	if (!query_only && backend->early_parse) {
 		printer_type = backend->early_parse(backend_ctx, data_fd);
 		if (printer_type < 0) {
-			ret = 4;
+			ret = 5; /* CUPS_BACKEND_CANCEL */
 			goto done;
 		}
 	}
@@ -520,7 +520,7 @@ int main (int argc, char **argv)
 
 	if (found == -1) {
 		ERROR("Printer open failure (No suitable printers found!)\n");
-		ret = 3;
+		ret = 4; /* CUPS_BACKEND_STOP */
 		goto done;
 	}
 
diff --git a/backend_shinkos2145.c b/backend_shinkos2145.c
index fcb6f8d..efe54a1 100644
--- a/backend_shinkos2145.c
+++ b/backend_shinkos2145.c
@@ -1617,7 +1617,7 @@ printer_error:
 	      status_str(sts->hdr.status),
 	      sts->hdr.printer_major, sts->hdr.printer_minor,
 	      error_codes(sts->hdr.printer_major, sts->hdr.printer_minor));
-	return 1;
+	return 1; /* CUPS_BACKEND_FAILED */
 }
 
 static int shinkos2145_query_serno(struct libusb_device_handle *dev, uint8_t endp_up, uint8_t endp_down, char *buf, int buf_len)