diff --git a/rtengine/imagesource.h b/rtengine/imagesource.h
index 25c024ed2..6cb279efc 100644
--- a/rtengine/imagesource.h
+++ b/rtengine/imagesource.h
@@ -171,7 +171,7 @@ public:
         outCurve = { 0.0 };
     }
     
-    double getDirPyrDenoiseExpComp ( )
+    double getDirPyrDenoiseExpComp () const
     {
         return dirpyrdenoiseExpComp;
     }