diff --git a/nread.c b/nread.c
index a7948974..e0ea5f07 100644
--- a/nread.c
+++ b/nread.c
@@ -294,15 +294,25 @@ static int NetReadRead(pNetRead self, pNetItem pItem)
         *pEnd = '\0';
         /* do we have something in hold ? */
         if (strlen(pItem->pHold) > 0) {
-          strlcat(pItem->pHold, pPtr,511);
-          iStat = CostaTop(pItem->pCon->pStack, pItem->pHold);
+          strlcat(pItem->pHold, pPtr, 511);
+          /* DFC locking for protocol zero only */
+          if (pItem->pCon->iProtocolID == 0 &&
+              CostaLocked(pItem->pCon->pStack))
+            iStat = 0;
+          else
+            iStat = CostaTop(pItem->pCon->pStack, pItem->pHold);
           if (!iStat) {
             SCWrite(pItem->pCon, "ERROR: Busy", eError);
           }
           pItem->pHold[0] = '\0';
         } else {
           /* no, normal command */
-          iStat = CostaTop(pItem->pCon->pStack, pPtr);
+          /* DFC locking for protocol zero only */
+          if (pItem->pCon->iProtocolID == 0 &&
+              CostaLocked(pItem->pCon->pStack))
+            iStat = 0;
+          else
+            iStat = CostaTop(pItem->pCon->pStack, pPtr);
           if (!iStat) {
             SCWrite(pItem->pCon, "ERROR: Busy", eError);
           }
@@ -487,7 +497,12 @@ static int TelnetRead(pNetRead self, pNetItem pItem)
         break;
       case '\r':
       case '\n':
-        iStat = CostaTop(pItem->pCon->pStack, pItem->pHold);
+        /* DFC locking for protocol zero only */
+        if (pItem->pCon->iProtocolID == 0 &&
+            CostaLocked(pItem->pCon->pStack))
+          iStat = 0;
+        else
+          iStat = CostaTop(pItem->pCon->pStack, pItem->pHold);
         /* printf("%s\n",pItem->pHold); */
         if (!iStat) {
           SCWrite(pItem->pCon, "ERROR: Busy", eError);