diff -r 286030fb113a -r c58fb5ed5a39 src/mem/bus.hh
--- a/src/mem/bus.hh	Mon Feb 13 11:55:51 2012 +0000
+++ b/src/mem/bus.hh	Mon Feb 13 11:56:31 2012 +0000
@@ -65,6 +65,10 @@
 #include "params/Bus.hh"
 #include "sim/eventq.hh"
 
+
+/** A symbolic name for a port id that denotes no port. */
+const short INVALID_PORT_ID = -1;
+
 class Bus : public MemObject
 {
     /** Declaration of the buses port type, one will be instantiated for each
@@ -220,7 +224,7 @@
             return portCache[2].id;
         }
 
-        return -1;
+        return INVALID_PORT_ID;
     }
 
     // Clears the earliest entry of the cache and inserts a new port entry
diff -r 286030fb113a -r c58fb5ed5a39 src/mem/bus.cc
--- a/src/mem/bus.cc	Mon Feb 13 11:55:51 2012 +0000
+++ b/src/mem/bus.cc	Mon Feb 13 11:56:31 2012 +0000
@@ -56,8 +56,9 @@
 Bus::Bus(const BusParams *p)
     : MemObject(p), busId(p->bus_id), clock(p->clock),
       headerCycles(p->header_cycles), width(p->width), tickNextIdle(0),
-      drainEvent(NULL), busIdle(this), inRetry(false), defaultPortId(-1),
-      useDefaultRange(p->use_default_range), defaultBlockSize(p->block_size),
+      drainEvent(NULL), busIdle(this), inRetry(false),
+      defaultPortId(INVALID_PORT_ID), useDefaultRange(p->use_default_range),
+      defaultBlockSize(p->block_size),
       cachedBlockSize(0), cachedBlockSizeValid(false)
 {
     //width, clock period, and header cycles must be positive
@@ -76,7 +77,7 @@
     std::string portName;
     int id = interfaces.size();
     if (if_name == "default") {
-        if (defaultPortId == -1) {
+        if (defaultPortId == INVALID_PORT_ID) {
             defaultPortId = id;
             portName = csprintf("%s-default", name());
         } else
@@ -301,7 +302,7 @@
     int dest_id;
 
     dest_id = checkPortCache(addr);
-    if (dest_id != -1)
+    if (dest_id != INVALID_PORT_ID)
         return dest_id;
 
     // Check normal port ranges
@@ -325,9 +326,16 @@
         panic("Unable to find destination for addr %#llx\n", addr);
     }
 
-    DPRINTF(Bus, "Unable to find destination for addr %#llx, "
-            "will use default port\n", addr);
-    return defaultPortId;
+    if (defaultPortId != INVALID_PORT_ID) {
+        DPRINTF(Bus, "Unable to find destination for addr %#llx, "
+                "will use default port\n", addr);
+        return defaultPortId;
+    } else {
+        panic("Unable to find destination for addr %#llx and no default "
+              "port set\n", addr);
+    }
+
+
 }