Index: trunk/src/oauth/signpost/signature/SignatureBaseString.java
===================================================================
--- trunk/src/oauth/signpost/signature/SignatureBaseString.java	(revision 4231)
+++ trunk/src/oauth/signpost/signature/SignatureBaseString.java	(revision 6849)
@@ -111,5 +111,7 @@
             }
 
-            sb.append(requestParameters.getAsQueryString(param));
+            // fix contributed by Stjepan Rajko
+            // since param should already be encoded, we supply false for percentEncode
+            sb.append(requestParameters.getAsQueryString(param, false));  
         }
         return sb.toString();