diff --git a/poll-billing.php b/poll-billing.php
index 01d615836a..f7e4b4f561 100755
--- a/poll-billing.php
+++ b/poll-billing.php
@@ -75,7 +75,7 @@ function CollectData($bill_id) {
 
             $tmp_period = dbFetchCell("SELECT UNIX_TIMESTAMP(CURRENT_TIMESTAMP()) - UNIX_TIMESTAMP('".mres($last_counters['timestamp'])."')");
 
-            if (delta_to_bits($port_data['in_delta'], $tmp_period) > $port_data['ifSpeed']) {
+            if (delta_to_bits($port_data['in_measurement'], $tmp_period)-$port_data['last_in_measurement'] > $port_data['ifSpeed']) {
                 $port_data['in_delta'] = $port_data['last_in_delta'];
             }
             elseif ($port_data['in_measurement'] >= $port_data['last_in_measurement']) {
@@ -85,7 +85,7 @@ function CollectData($bill_id) {
                 $port_data['in_delta'] = $port_data['last_in_delta'];
             }
             
-            if (delta_to_bits($port_data['out_delta'], $tmp_period) > $port_data['ifSpeed']) {
+            if (delta_to_bits($port_data['out_measurement'], $tmp_period)-$port_data['last_out_measurement'] > $port_data['ifSpeed']) {
                 $port_data['out_delta'] = $port_data['last_out_delta'];
             }
             elseif ($port_data['out_measurement'] >= $port_data['last_out_measurement']) {