diff --git a/src/sbcast/opts.c b/src/sbcast/opts.c
index 8c176432adbbf314a8e81f78813b0413b641484d..45b2baa64a831933c8c029294a8a66440c65d028 100644
--- a/src/sbcast/opts.c
+++ b/src/sbcast/opts.c
@@ -109,6 +109,8 @@ extern void parse_command_line(int argc, char *argv[])
 		params.preserve = true;
 	if ( ( env_val = getenv("SBCAST_SIZE") ) )
 		params.block_size = _map_size(env_val);
+	else
+		params.block_size = 8 * 1024 * 1024;
 	if ( ( env_val = getenv("SBCAST_TIMEOUT") ) )
 		params.timeout = (atoi(env_val) * 1000);