diff --git a/reactos/drivers/input/mouclass/mouclass.c b/reactos/drivers/input/mouclass/mouclass.c
index a6b6ed414cf..a49074b651a 100644
--- a/reactos/drivers/input/mouclass/mouclass.c
+++ b/reactos/drivers/input/mouclass/mouclass.c
@@ -671,7 +671,7 @@ ClassAddDevice(
 	}
 
 	DeviceExtension = (PPORT_DEVICE_EXTENSION)Fdo->DeviceExtension;
-	RtlZeroMemory(DeviceExtension, sizeof(CLASS_DEVICE_EXTENSION));
+	RtlZeroMemory(DeviceExtension, sizeof(PORT_DEVICE_EXTENSION));
 	DeviceExtension->Common.IsClassDO = FALSE;
 	DeviceExtension->DeviceObject = Fdo;
 	DeviceExtension->PnpState = dsStopped;