diff --git a/src/cpu/thread_state.hh b/src/cpu/thread_state.hh
--- a/src/cpu/thread_state.hh
+++ b/src/cpu/thread_state.hh
@@ -99,13 +99,13 @@
 
     TheISA::Kernel::Statistics *getKernelStats() { return kernelStats; }
 
-    PortProxy &getPhysProxy() { return *physProxy; }
+    PortProxy &getPhysProxy();
 
-    FSTranslatingPortProxy &getVirtProxy() { return *virtProxy; }
+    FSTranslatingPortProxy &getVirtProxy();
 
     Process *getProcessPtr() { return process; }
 
-    SETranslatingPortProxy &getMemProxy() { return *proxy; }
+    SETranslatingPortProxy &getMemProxy();
 
     /** Reads the number of instructions functionally executed and
      * committed.
diff --git a/src/cpu/thread_state.cc b/src/cpu/thread_state.cc
--- a/src/cpu/thread_state.cc
+++ b/src/cpu/thread_state.cc
@@ -122,6 +122,30 @@
     }
 }
 
+PortProxy &
+ThreadState::getPhysProxy()
+{
+    assert(FullSystem);
+    assert(physProxy != NULL);
+    return *physProxy;
+}
+
+FSTranslatingPortProxy &
+ThreadState::getVirtProxy()
+{
+    assert(FullSystem);
+    assert(virtProxy != NULL);
+    return *virtProxy;
+}
+
+SETranslatingPortProxy &
+ThreadState::getMemProxy()
+{
+    assert(!FullSystem);
+    assert(proxy != NULL);
+    return *proxy;
+}
+
 void
 ThreadState::profileClear()
 {