diff --git a/src/dev/io_device.cc b/src/dev/io_device.cc
index b118294f7..a536e2973 100644
--- a/src/dev/io_device.cc
+++ b/src/dev/io_device.cc
@@ -57,7 +57,9 @@ PioPort::recvAtomic(PacketPtr pkt)
     // @todo: We need to pay for this and not just zero it out
     pkt->firstWordDelay = pkt->lastWordDelay = 0;
 
-    return pkt->isRead() ? device->read(pkt) : device->write(pkt);
+    const Tick delay(pkt->isRead() ? device->read(pkt) : device->write(pkt));
+    assert(pkt->isResponse() || pkt->isError());
+    return delay;
 }
 
 AddrRangeList