--- a/dwt/dwthelper/utils.d	Sun Nov 30 09:25:27 2008 +0100
+++ b/dwt/dwthelper/utils.d	Sun Nov 30 09:42:03 2008 +0100
@@ -487,8 +487,25 @@
         return index;
     }
     else{
+        int steps = 0;
         while(( str[index] & 0xC0 ) is 0x80 ){
             index--;
+            steps++;
+            if( steps > 3 || index < 0 ){
+                break;
+            }
+        }
+        if((( str[index] & 0xE0 ) is 0xC0) && ( steps <= 1 )){
+            // ok
+        }
+        else if((( str[index] & 0xF0 ) is 0xE0) && ( steps <= 2 )){
+            // ok
+        }
+        else if((( str[index] & 0xF8 ) is 0xF0) && ( steps <= 3 )){
+            // ok
+        }
+        else{
+            tango.text.convert.Utf.onUnicodeError( "invalid utf8 input to toAbsoluteCodePointStartOffset" );
         }
         return index;
     }