diff --git a/lib/MongoDB/_Topology.pm b/lib/MongoDB/_Topology.pm
index 989fa408..a2c5d012 100644
--- a/lib/MongoDB/_Topology.pm
+++ b/lib/MongoDB/_Topology.pm
@@ -829,6 +829,8 @@ sub _get_server_in_latency_window {
     return $in_window[ int( rand(@in_window) ) ]->{server};
 }
 
+my $PRIMARY = MongoDB::ReadPreference->new(mode => 'primaryPreferred' );
+
 sub _ping_server {
     my ($self, $link) = @_;
     return eval {
@@ -837,7 +839,7 @@ sub _ping_server {
             query               => [ping => 1],
             query_flags         => {},
             bson_codec          => $self->bson_codec,
-            read_preference     => 'primaryPreferred',
+            read_preference     => $PRIMARY,
             monitoring_callback => $self->monitoring_callback,
         );
         $op->execute( $link )->output;
@@ -1037,8 +1039,6 @@ sub _selection_timeout {
     }
 }
 
-my $PRIMARY = MongoDB::ReadPreference->new;
-
 sub _generate_ismaster_request {
     my ( $self, $link, $should_perform_handshake ) = @_;
     my @opts;