1 files changed, 8 insertions, 0 deletions
diff --git a/src/mongo/db/repl/repl_set_heartbeat_response.cpp b/src/mongo/db/repl/repl_set_heartbeat_response.cpp
index c43316acdc0..5905881ac3d 100644
--- a/src/mongo/db/repl/repl_set_heartbeat_response.cpp
+++ b/src/mongo/db/repl/repl_set_heartbeat_response.cpp
@@ -51,6 +51,7 @@ namespace {
 
 const std::string kConfigFieldName = "config";
 const std::string kConfigVersionFieldName = "v";
+const std::string kConfigTermFieldName = "t";
 const std::string kElectionTimeFieldName = "electionTime";
 const std::string kMemberStateFieldName = "state";
 const std::string kOkFieldName = "ok";
@@ -80,6 +81,7 @@ void ReplSetHeartbeatResponse::addToBSON(BSONObjBuilder* builder) const {
     }
     if (_configVersion != -1) {
         *builder << kConfigVersionFieldName << _configVersion;
+        *builder << kConfigTermFieldName << _configTerm;
     }
     if (!_setName.empty()) {
         *builder << kReplSetFieldName << _setName;
@@ -218,6 +220,12 @@ Status ReplSetHeartbeatResponse::initialize(const BSONObj& doc, long long term)
     }
     _configVersion = configVersionElement.numberInt();
 
+    // Allow a missing term field for backward compatibility.
+    const BSONElement configTermElement = doc[kConfigTermFieldName];
+    if (!configTermElement.eoo() && configVersionElement.type() == NumberInt) {
+        _configTerm = configTermElement.numberInt();
+    }
+
     const BSONElement syncingToElement = doc[kSyncSourceFieldName];
     if (syncingToElement.eoo()) {
         _syncingTo = HostAndPort();