diff --git a/src/Filter.cpp b/src/Filter.cpp
index 6f3f572dd..ab11bb8a5 100644
--- a/src/Filter.cpp
+++ b/src/Filter.cpp
@@ -40,10 +40,10 @@ extern Context context;
 ////////////////////////////////////////////////////////////////////////////////
 // Const iterator that can be derefenced into a Task by domSource.
 static Task dummy;
-static Task& contextTask = dummy;
+Task& contextTask = dummy;
 
 ////////////////////////////////////////////////////////////////////////////////
-static bool domSource (const std::string& identifier, Variant& value)
+bool domSource (const std::string& identifier, Variant& value)
 {
   std::string stringValue = context.dom.get (identifier, contextTask);
   if (stringValue != identifier)
diff --git a/src/Filter.h b/src/Filter.h
index 2d2b0bec8..e51dc2ef6 100644
--- a/src/Filter.h
+++ b/src/Filter.h
@@ -27,8 +27,12 @@
 #ifndef INCLUDED_FILTER
 #define INCLUDED_FILTER
 
+#include <string>
 #include <vector>
 #include <Task.h>
+#include <Variant.h>
+
+bool domSource (const std::string&, Variant&);
 
 class Filter
 {