diff --git a/src/polar/v2/trainingsession.cpp b/src/polar/v2/trainingsession.cpp
index 760f3927..5118c5cf 100644
--- a/src/polar/v2/trainingsession.cpp
+++ b/src/polar/v2/trainingsession.cpp
@@ -2102,7 +2102,7 @@ QDomDocument TrainingSession::toTCX(const QString &buildTime) const
         QVariantMap base = create; // The base data for this lap.
         QVariantMap stats = map.value(STATISTICS).toMap();
         QDomElement track = doc.createElement(QLatin1String("Track"));
-        qint64 durationRemaining = getDuration(firstMap(create.value(QLatin1String("duration"))));
+        quint64 durationRemaining = getDuration(firstMap(create.value(QLatin1String("duration"))));
         double distanceRemaining = first(create.value(QLatin1String("distance"))).toDouble();
         for (int index = 0; index < maxIndex; ++index) {
             #if (QT_VERSION >= QT_VERSION_CHECK(5, 2, 0))
@@ -2110,7 +2110,8 @@ QDomDocument TrainingSession::toTCX(const QString &buildTime) const
             #else
             if ((lap.isNull()) || ((!splits.isEmpty()) && (index * recordInterval > splits.constBegin().key()))) {
             #endif
-                double trailingDuration = 0, trailingDistance = 0;
+                quint64 trailingDuration = 0;
+                double trailingDistance = 0.0;
                 if ((!lap.isNull()) && (!splits.isEmpty())) {
                     #if (QT_VERSION >= QT_VERSION_CHECK(5, 2, 0))
                     splits.remove(splits.firstKey());
@@ -2152,8 +2153,7 @@ QDomDocument TrainingSession::toTCX(const QString &buildTime) const
                 activity.appendChild(lap);
 
                 // Add the per-lap (or per-exercise) statistics.
-                addLapStats(doc, lap, base, stats, trailingDuration / 1000.0,
-                            trailingDistance);
+                addLapStats(doc, lap, base, stats, trailingDuration, trailingDistance);
 
                 track = doc.createElement(QLatin1String("Track"));
                 lap.appendChild(track);
@@ -2399,12 +2399,22 @@ QDomDocument TrainingSession::toTCX(const QString &buildTime) const
 void TrainingSession::addLapStats(QDomDocument &doc, QDomElement &lap,
                                   const QVariantMap &base,
                                   const QVariantMap &stats,
-                                  const double duration,
+                                  const quint64 duration,
                                   const double distance) const
 {
+    // Note, we're using an explicit precision argument to QString::arg here
+    // because QString::arg defaults to the precision to -1, which in turn
+    // (within QLocale::doubleToString) defaults to a maximum of 6 significant
+    // digits (not decimal digits, as the QString::arg docs claim), which is not
+    // always enough for the TotalTimeSeconds value to be accurate to the
+    // millisecond data that the V800 provides.  We use 20 digits here, since
+    // that's the maximum that could ever be present in a quint64 integer,
+    // however that's likely to be massive overkill for our use case (but does
+    // no harm, since only the necessary digits are printed anyway).
     lap.appendChild(doc.createElement(QLatin1String("TotalTimeSeconds")))
-        .appendChild(doc.createTextNode(QString::fromLatin1("%1").arg(qMax(
-            duration, getDuration(firstMap(base.value(QLatin1String("duration"))))/1000.0))));
+        .appendChild(doc.createTextNode(QString::fromLatin1("%1").arg(
+            qMax(duration, getDuration(firstMap(base.value(QLatin1String("duration")))))/1000.0,
+            0, 'g', 20))); // Since quint64 can have supply more than 20 digits.
     lap.appendChild(doc.createElement(QLatin1String("DistanceMeters")))
         .appendChild(doc.createTextNode(QString::fromLatin1("%1").arg(qMax(
             distance, first(base.value(QLatin1String("distance"))).toDouble()))));
diff --git a/src/polar/v2/trainingsession.h b/src/polar/v2/trainingsession.h
index 9a99d864..95a6d7ab 100644
--- a/src/polar/v2/trainingsession.h
+++ b/src/polar/v2/trainingsession.h
@@ -152,7 +152,7 @@ class TrainingSession : public QObject {
 
     void addLapStats(QDomDocument &doc, QDomElement &lap,
                      const QVariantMap &base, const QVariantMap &stats,
-                     const double duration = 0, const double distance = 0) const;
+                     const quint64 duration = 0, const double distance = 0) const;
 
 };
 
diff --git a/test/polar/v2/testdata/training-sessions-19401412.tcx b/test/polar/v2/testdata/training-sessions-19401412.tcx
index b7427541..4eb6c49c 100644
--- a/test/polar/v2/testdata/training-sessions-19401412.tcx
+++ b/test/polar/v2/testdata/training-sessions-19401412.tcx
@@ -4,7 +4,7 @@
     <Activity Sport="Running">
       <Id>2014-07-13T07:26:23+10:00</Id>
       <Lap StartTime="2014-07-13T07:26:23+10:00">
-        <TotalTimeSeconds>1803.88</TotalTimeSeconds>
+        <TotalTimeSeconds>1803.875</TotalTimeSeconds>
         <DistanceMeters>2941.6</DistanceMeters>
         <MaximumSpeed>13.896</MaximumSpeed>
         <Calories>0</Calories>
@@ -42340,7 +42340,7 @@
         </Track>
       </Lap>
       <Lap StartTime="2014-07-13T08:25:07+10:00">
-        <TotalTimeSeconds>1561.62</TotalTimeSeconds>
+        <TotalTimeSeconds>1561.625</TotalTimeSeconds>
         <DistanceMeters>2594.9</DistanceMeters>
         <MaximumSpeed>12.888</MaximumSpeed>
         <Calories>0</Calories>