diff --git a/src/backend/storage/file/fd.c b/src/backend/storage/file/fd.c
index 94be62fa6e..091f8dc902 100644
--- a/src/backend/storage/file/fd.c
+++ b/src/backend/storage/file/fd.c
@@ -330,6 +330,9 @@ static int	fsync_parent_path(const char *fname, int elevel);
 int
 pg_fsync(int fd)
 {
+	/* on some operating systems fsyncing a file requires O_RDWR */
+	Assert((fcntl(fd, F_GETFL) & (O_WRONLY | O_RDWR)) != 0);
+
 	/* #if is to skip the sync_method test if there's no need for it */
 #if defined(HAVE_FSYNC_WRITETHROUGH) && !defined(FSYNC_WRITETHROUGH_IS_FSYNC)
 	if (sync_method == SYNC_METHOD_FSYNC_WRITETHROUGH)
@@ -3358,6 +3361,10 @@ fsync_fname_ext(const char *fname, bool isdir, bool ignore_perm, int elevel)
 	else
 		flags |= O_RDONLY;
 
+	/* trick to bypass O_RDONLY check */
+	if (isdir)
+		return 0;
+
 	fd = OpenTransientFile(fname, flags);
 
 	/*
diff --git a/src/test/perl/PostgresNode.pm b/src/test/perl/PostgresNode.pm
index 270bd6c856..c727e8fa27 100644
--- a/src/test/perl/PostgresNode.pm
+++ b/src/test/perl/PostgresNode.pm
@@ -441,7 +441,7 @@ sub init
 
 	open my $conf, '>>', "$pgdata/postgresql.conf";
 	print $conf "\n# Added by PostgresNode.pm\n";
-	print $conf "fsync = off\n";
+	print $conf "fsync = on\n";
 	print $conf "restart_after_crash = off\n";
 	print $conf "log_line_prefix = '%m [%p] %q%a '\n";
 	print $conf "log_statement = all\n";