diff --git a/rtgui/previewloader.cc b/rtgui/previewloader.cc
index f4cfe2b1b..34b42dcb7 100644
--- a/rtgui/previewloader.cc
+++ b/rtgui/previewloader.cc
@@ -59,7 +59,7 @@ public:
         };
     */
     struct JobCompare {
-        bool operator()(const Job& lhs, const Job& rhs)
+        bool operator()(const Job& lhs, const Job& rhs) const
         {
             if ( lhs.dir_id_ == rhs.dir_id_ ) {
                 return lhs.dir_entry_ < rhs.dir_entry_;