--- a/dom/plugins/test/testplugin/nptest.cpp
+++ b/dom/plugins/test/testplugin/nptest.cpp
@@ -522,17 +522,17 @@ static void sendBufferToFrame(NPP instan
         outbuf.replace(i, 1, "");
         i -= 1;
       }
       else {
         int ascii = outbuf[i];
         if (!((ascii >= ',' && ascii <= ';') ||
               (ascii >= 'A' && ascii <= 'Z') ||
               (ascii >= 'a' && ascii <= 'z'))) {
-          char hex[8];
+          char hex[10];
           sprintf(hex, "%%%x", ascii);
           outbuf.replace(i, 1, hex);
           i += 2;
         }
       }
     }
 
     NPError err = NPN_GetURL(instance, outbuf.c_str(),