diff --git a/fb/fbblt.c b/fb/fbblt.c
index a040298..6809404 100644
--- a/fb/fbblt.c
+++ b/fb/fbblt.c
@@ -65,6 +65,7 @@ fbBlt (FbBits   *srcLine,
     int	    n, nmiddle;
     Bool    destInvarient;
     int	    startbyte, endbyte;
+    int     careful;
     FbDeclareMergeRop ();
 
     if (bpp == 24 && !FbCheck24Pix (pm))
@@ -74,12 +75,16 @@ fbBlt (FbBits   *srcLine,
 	return;
     }
 
-    if (alu == GXcopy && pm == FB_ALLONES && !reverse &&
+    careful = !((srcLine < dstLine && srcLine + width * (bpp>>3) > dstLine) ||
+                (dstLine < srcLine && dstLine + width * (bpp>>3) > srcLine)) ||
+              (bpp & 7);
+
+    if (alu == GXcopy && pm == FB_ALLONES && !careful &&
             !(srcX & 7) && !(dstX & 7) && !(width & 7)) {
         int i;
         CARD8 *src = (CARD8 *) srcLine;
         CARD8 *dst = (CARD8 *) dstLine;
-        
+
         srcStride *= sizeof(FbBits);
         dstStride *= sizeof(FbBits);
         width >>= 3;