diff --git a/bacnet-stack/ports/atmega168/device.h b/bacnet-stack/ports/atmega168/device.h
index 6516d6bc..d0d45609 100644
--- a/bacnet-stack/ports/atmega168/device.h
+++ b/bacnet-stack/ports/atmega168/device.h
@@ -153,7 +153,7 @@ extern "C" {
         uint8_t * apdu,
         uint32_t object_instance,
         BACNET_PROPERTY_ID property,
-        int32_t array_index,
+        uint32_t array_index,
         BACNET_ERROR_CLASS * error_class,
         BACNET_ERROR_CODE * error_code);