--- old/src/java.httpclient/share/classes/java/net/http/HttpHeadersImpl.java	Fri Mar  4 11:51:30 2016
+++ new/src/java.httpclient/share/classes/java/net/http/HttpHeadersImpl.java	Fri Mar  4 11:51:30 2016
@@ -72,7 +72,7 @@
 
     @Override
     public List<String> allValues(String name) {
-        return headers.get(name);
+        return Collections.unmodifiableList(headers.get(name));
     }
 
     @Override