diff --git a/sys/cam/mmc/mmc_da.c b/sys/cam/mmc/mmc_da.c
--- a/sys/cam/mmc/mmc_da.c
+++ b/sys/cam/mmc/mmc_da.c
@@ -1178,6 +1178,8 @@
 		return ("4-bit");
 	case bus_width_8:
 		return ("8-bit");
+	default:
+		__assert_unreachable();
 	}
 }