diff --git a/src/cpu/o3/cpu.cc b/src/cpu/o3/cpu.cc
index dfe42d882..580816372 100644
--- a/src/cpu/o3/cpu.cc
+++ b/src/cpu/o3/cpu.cc
@@ -819,6 +819,12 @@ unsigned int
 FullO3CPU<Impl>::drain(Event *drain_event)
 {
     DPRINTF(O3CPU, "Switching out\n");
+
+    // If the CPU isn't doing anything, then return immediately.
+    if (_status == Idle || _status == SwitchedOut) {
+        return 0;
+    }
+
     drainCount = 0;
     fetch.drain();
     decode.drain();
diff --git a/src/cpu/simple/atomic.cc b/src/cpu/simple/atomic.cc
index 4f68cfd6f..f94ea0917 100644
--- a/src/cpu/simple/atomic.cc
+++ b/src/cpu/simple/atomic.cc
@@ -213,6 +213,9 @@ AtomicSimpleCPU::takeOverFrom(BaseCPU *oldCPU)
             break;
         }
     }
+    if (_status != Running) {
+        _status = Idle;
+    }
 }
 
 
diff --git a/src/mem/bus.cc b/src/mem/bus.cc
index 7b65d252b..ae87d8099 100644
--- a/src/mem/bus.cc
+++ b/src/mem/bus.cc
@@ -242,8 +242,11 @@ Bus::recvRetry(int id)
         }
     }
     //If we weren't able to drain before, we might be able to now.
-    if (drainEvent && retryList.size() == 0 && curTick >= tickNextIdle)
+    if (drainEvent && retryList.size() == 0 && curTick >= tickNextIdle) {
         drainEvent->process();
+        // Clear the drain event once we're done with it.
+        drainEvent = NULL;
+    }
 }
 
 Port *