diff --git a/core/src/main/java/hudson/Functions.java b/core/src/main/java/hudson/Functions.java
index aadecaa51c..ed01810067 100644
--- a/core/src/main/java/hudson/Functions.java
+++ b/core/src/main/java/hudson/Functions.java
@@ -138,10 +138,7 @@ public class Functions {
             if(n ==null)
                 return null;
             else {
-                String url = contextPath + '/' + n.getUrl();
-                assert url.endsWith("/");
-                url = url.substring(0,url.length()-1);  // cut off the trailing '/'
-                return url+rest;
+                return basePortion+"/../"+n.getNumber()+rest;
             }
         }
     }
diff --git a/core/src/main/resources/hudson/model/Build/sidepanel.jelly b/core/src/main/resources/hudson/model/Build/sidepanel.jelly
index 4aa5f2dff8..64133a1786 100644
--- a/core/src/main/resources/hudson/model/Build/sidepanel.jelly
+++ b/core/src/main/resources/hudson/model/Build/sidepanel.jelly
@@ -6,7 +6,7 @@
   <l:side-panel>
     <l:tasks>
       <j:set var="buildUrl" value="${h.decompose(request)}" />
-      <l:task icon="images/24x24/up.gif" href="${rootURL}/${it.parent.url}" title="Back to Project" />
+      <l:task icon="images/24x24/up.gif" href="${h.getNearestAncestorUrl(request,it.parent)}/" title="Back to Project" />
       <l:task icon="images/24x24/search.gif" href="${buildUrl.baseUrl}/" title="Status" />
       <l:task icon="images/24x24/notepad.gif" href="${buildUrl.baseUrl}/changes" title="Changes" />
       <j:choose>