diff --git a/rtgui/histogrampanel.cc b/rtgui/histogrampanel.cc
index 3c784a96b..98651ca0d 100644
--- a/rtgui/histogrampanel.cc
+++ b/rtgui/histogrampanel.cc
@@ -908,6 +908,7 @@ int histupdateUI (void* data)
         return 0;
     }
 
+    haih->harea->setDirty (true);
     haih->harea->updateBackBuffer ();
     haih->harea->queue_draw ();