diff --git a/common/rfb/Configuration.h b/common/rfb/Configuration.h
index da93fdd..fbf161d 100644
--- a/common/rfb/Configuration.h
+++ b/common/rfb/Configuration.h
@@ -45,6 +45,8 @@
 
 #include <rfb/util.h>
 
+namespace os { class Mutex; }
+
 namespace rfb {
   class VoidParameter;
   struct ParameterIterator;
@@ -174,6 +176,8 @@
     bool immutable;
     const char* name;
     const char* description;
+
+    os::Mutex* mutex;
   };
 
   class AliasParameter : public VoidParameter {