diff --git a/src/dev/isa_fake.cc b/src/dev/isa_fake.cc
index 81c7a4dcd..235dc3098 100644
--- a/src/dev/isa_fake.cc
+++ b/src/dev/isa_fake.cc
@@ -110,7 +110,7 @@ IsaFake::write(PacketPtr pkt)
             data = pkt->get<uint8_t>();
             break;
           default:
-            panic("invalid access size!\n");
+            panic("invalid access size: %u\n", pkt->getSize());
         }
         warn("Device %s accessed by write to address %#x size=%d data=%#x\n",
                 name(), pkt->getAddr(), pkt->getSize(), data);