lib/PublicInbox/SearchIdx.pm | 3 ++-

diff --git a/lib/PublicInbox/SearchIdx.pm b/lib/PublicInbox/SearchIdx.pm
index 04e853069f0661c24b5d223d2c1ad72f47e7232b..bb60506ce1a9996e1d6a9971e61459cf13b250b7 100644
--- a/lib/PublicInbox/SearchIdx.pm
+++ b/lib/PublicInbox/SearchIdx.pm
@@ -22,7 +22,8 @@ require PublicInbox::Git;
 use Compress::Zlib qw(compress);
 
 use constant {
-	BATCH_BYTES => 1_000_000,
+	BATCH_BYTES => defined($ENV{XAPIAN_FLUSH_THRESHOLD}) ?
+			0x7fffffff : 1_000_000,
 	DEBUG => !!$ENV{DEBUG},
 };