diff --git a/src/bin/pg_upgrade/t/002_pg_upgrade.pl b/src/bin/pg_upgrade/t/002_pg_upgrade.pl
index c6d83d3c21..d34b45e346 100644
--- a/src/bin/pg_upgrade/t/002_pg_upgrade.pl
+++ b/src/bin/pg_upgrade/t/002_pg_upgrade.pl
@@ -293,6 +293,7 @@ if (defined($ENV{oldinstall}))
 	}
 
 	open my $fh, ">", $dump1_file or die "could not open dump file";
+	binmode $fh;
 	print $fh $dump_data;
 	close $fh;