jaxp/src/java.xml/share/classes/com/sun/org/apache/xalan/internal/xsltc/runtime/BasisLibrary.java

@@ -290,11 +290,12 @@
      * conversions resulting into NaNs and rounding.
      */
     public static String substringF(String value, double start, double length) {
         if (Double.isInfinite(start) ||
             Double.isNaN(start) ||
-            Double.isNaN(length))
+            Double.isNaN(length) ||
+            length < 0)
             return(EMPTYSTRING);
 
             int istart = (int)Math.round(start) - 1;
         final int isum;
         if (Double.isInfinite(length))