diff --git a/plugins/datasource-zabbix/dataProcessingService.js b/plugins/datasource-zabbix/dataProcessingService.js
index d3972d9..e0be758 100644
--- a/plugins/datasource-zabbix/dataProcessingService.js
+++ b/plugins/datasource-zabbix/dataProcessingService.js
@@ -69,9 +69,16 @@ function (angular, _, moment, utils) {
      */
     this.groupBy = function(interval, groupByCallback, datapoints) {
       var ms_interval = utils.parseInterval(interval);
+
+      // Calculate frame timestamps
+      var min_timestamp = datapoints[0][1];
       var frames = _.groupBy(datapoints, function(point) {
-        var group_time = Number(moment.utc(point[1]).startOf('minute').valueOf());
-        group_time = Math.ceil(point[1] / ms_interval) * ms_interval;
+        var group_time = Math.floor(point[1] / ms_interval) * ms_interval;
+
+        // Prevent points outside of time range
+        if (group_time < min_timestamp) {
+          group_time = min_timestamp;
+        }
         return group_time;
       });