diff --git a/src/driver/tpax_driver_ctx.c b/src/driver/tpax_driver_ctx.c
index b1393d2..6bb7545 100644
--- a/src/driver/tpax_driver_ctx.c
+++ b/src/driver/tpax_driver_ctx.c
@@ -242,6 +242,22 @@ static int tpax_driver_usage_block_size_range(
 	return TPAX_USAGE;
 }
 
+static int tpax_driver_usage_block_constraints(
+	int				fdout,
+	const char *			program,
+	const char *			arg,
+	struct argv_meta *		meta)
+{
+	tpax_dprintf(
+		fdout,
+		"%s: usage error: the specified block size `%s' is not a multiple of 512 bytes.\n",
+		program,arg);
+
+	argv_free(meta);
+
+	return TPAX_USAGE;
+}
+
 static int tpax_driver_error_archive_path(
 	int				fdout,
 	const char *			program,
@@ -480,6 +496,12 @@ int tpax_lib_get_driver_ctx(
 							fdctx->fderr,
 							program,entry->arg,
 							optv,meta);
+
+					if (cctx.blksize % 512)
+						return tpax_driver_usage_block_constraints(
+							fdctx->fderr,
+							program,entry->arg,
+							meta);
 					break;
 
 				case TAG_RECURSE: