diff --git a/src/ca/cac.cpp b/src/ca/cac.cpp
index df0eb881c..3e05461ab 100644
--- a/src/ca/cac.cpp
+++ b/src/ca/cac.cpp
@@ -1752,7 +1752,7 @@ void cac::privateUninstallIIU ( epicsGuard < callbackMutex > & cbGuard, tcpiiu &
     if ( iiu.channelCount() ) {
         char hostNameTmp[64];
         iiu.hostName ( hostNameTmp, sizeof ( hostNameTmp ) );
-        genLocalExcep ( *this, ECA_DISCONN, hostNameTmp );
+        genLocalExcep ( cbGuard, *this, ECA_DISCONN, hostNameTmp );
     }
     osiSockAddr addr = iiu.getNetworkAddress();
     if ( addr.sa.sa_family == AF_INET ) {
diff --git a/src/ca/cac.h b/src/ca/cac.h
index 49cf89683..77d400d06 100644
--- a/src/ca/cac.h
+++ b/src/ca/cac.h
@@ -151,8 +151,8 @@ public:
     void uninstallCASG ( CASG & );
 
     // exception generation
-    void exception ( int status, const char *pContext,
-        const char *pFileName, unsigned lineNo );
+    void exception ( epicsGuard < callbackMutex > &, int status, const char * pContext,
+        const char * pFileName, unsigned lineNo );
 
     // callback preemption control
     int blockForEventAndEnableCallbacks ( epicsEvent &event, double timeout );
@@ -340,8 +340,8 @@ inline cacMutex & cac::mutexRef ()
     return this->mutex;
 }
 
-inline void cac::exception ( int status, const char *pContext,
-    const char *pFileName, unsigned lineNo )
+inline void cac::exception ( epicsGuard < callbackMutex > &, int status, 
+    const char *pContext, const char *pFileName, unsigned lineNo )
 {
     this->notify.exception ( status, pContext, pFileName, lineNo );
 }
diff --git a/src/ca/iocinf.h b/src/ca/iocinf.h
index 25d3dacbc..d5c34ffc7 100644
--- a/src/ca/iocinf.h
+++ b/src/ca/iocinf.h
@@ -70,7 +70,7 @@ private:
 /*
  * CA internal functions
  */
-#define genLocalExcep( CAC, STAT, PCTX ) \
-(CAC).exception ( STAT, PCTX, __FILE__, __LINE__ )
+#define genLocalExcep( GUARD, CAC, STAT, PCTX ) \
+(CAC).exception ( GUARD, STAT, PCTX, __FILE__, __LINE__ )
 
 #endif // ifdef INCiocinfh 
diff --git a/src/ca/msgForMultiplyDefinedPV.cpp b/src/ca/msgForMultiplyDefinedPV.cpp
index 47ad593c5..f694ae0a9 100644
--- a/src/ca/msgForMultiplyDefinedPV.cpp
+++ b/src/ca/msgForMultiplyDefinedPV.cpp
@@ -45,6 +45,6 @@ void msgForMultiplyDefinedPV::ioCompletionNotify ( const char * pHostNameRej )
     char buf[256];
     sprintf ( buf, "Channel: \"%.64s\", Connecting to: %.64s, Ignored: %.64s",
             this->channel, this->acc, pHostNameRej );
-    epicsGuard < callbackMutex > guard ( this->mutex );
-    genLocalExcep ( this->cacRef, ECA_DBLCHNL, buf );
+    epicsGuard < callbackMutex > cbGuard ( this->mutex );
+    genLocalExcep ( cbGuard, this->cacRef, ECA_DBLCHNL, buf );
 }
diff --git a/src/ca/udpiiu.cpp b/src/ca/udpiiu.cpp
index ba485d535..9315a1f52 100644
--- a/src/ca/udpiiu.cpp
+++ b/src/ca/udpiiu.cpp
@@ -56,7 +56,7 @@ const udpiiu::pProtoStubUDP udpiiu::udpJumpTableCAC [] =
 //
 // udpiiu::udpiiu ()
 //
-udpiiu::udpiiu ( epicsTimerQueueActive &timerQueue, callbackMutex & cbMutex, cac & cac ) :
+udpiiu::udpiiu ( epicsTimerQueueActive & timerQueue, callbackMutex & cbMutex, cac & cac ) :
     recvThread ( *this, cbMutex,
         "CAC-UDP", 
         epicsThreadGetStackSize ( epicsThreadStackMedium ),
@@ -157,16 +157,8 @@ udpiiu::udpiiu ( epicsTimerQueueActive &timerQueue, callbackMutex & cbMutex, cac
      * load user and auto configured
      * broadcast address list
      */
-    ellInit ( &this->dest );    // X aCC 392
+    ellInit ( & this->dest );    // X aCC 392
     configureChannelAccessAddressList ( &this->dest, this->sock, this->serverPort );
-    if ( ellCount ( &this->dest ) == 0 ) { // X aCC 392
-        // no need to lock callbacks here because
-        // 1) this is called while in a CA client function
-        // 2) no auxiliary threads are running at this point
-        // (taking the callback lock here would break the
-        // lock hierarchy and risk deadlocks)
-        genLocalExcep ( this->cacRef, ECA_NOSEARCHADDR, NULL );
-    }
   
     caStartRepeaterIfNotInstalled ( this->repeaterPort );
 
@@ -300,6 +292,10 @@ void udpRecvThread::run ()
     {
         epicsGuard < callbackMutex > cbGuard ( this->cbMutex );
         this->iiu.cacRef.notifyNewFD ( cbGuard, this->iiu.sock );
+        if ( ellCount ( & this->iiu.dest ) == 0 ) { // X aCC 392
+            genLocalExcep ( cbGuard, this->iiu.cacRef, ECA_NOSEARCHADDR, NULL );
+        }
+
     }
 
     do {