diff --git a/scst/src/scst_lib.c b/scst/src/scst_lib.c
index 45c9d48ef..8f473809d 100644
--- a/scst/src/scst_lib.c
+++ b/scst/src/scst_lib.c
@@ -6843,6 +6843,7 @@ int scst_get_cdb_info(struct scst_cmd *cmd)
 		/* opcode not found or now not used */
 		TRACE(TRACE_MINOR, "Unknown opcode 0x%x for type %d", op,
 		      dev_type);
+		cmd->op_flags |= SCST_LBA_NOT_VALID;
 		res = -1;
 		goto out;
 	}