diff --git a/libvncclient/rfbproto.c b/libvncclient/rfbproto.c
index 721c3ae..e2a583c 100644
--- a/libvncclient/rfbproto.c
+++ b/libvncclient/rfbproto.c
@@ -167,6 +167,10 @@ static void FillRectangle(rfbClient* client, int x, int y, int w, int h, uint32_
 static void CopyRectangle(rfbClient* client, uint8_t* buffer, int x, int y, int w, int h) {
   int j;
 
+  if (client->frameBuffer == NULL) {
+      return;
+  }
+
 #define COPY_RECT(BPP) \
   { \
     int rs = w * BPP / 8, rs2 = client->width * BPP / 8; \
diff --git a/libvncclient/vncviewer.c b/libvncclient/vncviewer.c
index 4f87f01..af0a50b 100644
--- a/libvncclient/vncviewer.c
+++ b/libvncclient/vncviewer.c
@@ -154,6 +154,9 @@ rfbClient* rfbGetClient(int bitsPerSample,int samplesPerPixel,
   /* default: use complete frame buffer */ 
   client->updateRect.x = -1;
  
+  client->frameBuffer = NULL;
+  client->outputWindow = 0;
+ 
   client->format.bitsPerPixel = bytesPerPixel*8;
   client->format.depth = bitsPerSample*samplesPerPixel;
   client->appData.requestedDepth=client->format.depth;