diff --git a/snmp2mqtt.py b/snmp2mqtt.py
index 6cfac93..2e81496 100755
--- a/snmp2mqtt.py
+++ b/snmp2mqtt.py
@@ -286,6 +286,9 @@ def create_ha_sensor_config(req, oid):
     # Add device class if specified
     if 'HA_device_class' in oid:
         config['device_class'] = oid['HA_device_class']
+        # Add state_class for total_increasing counters like data size
+        if oid['HA_device_class'] == 'data_size':
+            config['state_class'] = 'total_increasing'
     
     # Add unit of measurement if specified
     if 'HA_unit' in oid: