diff --git a/src/widgets/ASlider.cpp b/src/widgets/ASlider.cpp
index 149d31e1c..c9c6c775f 100644
--- a/src/widgets/ASlider.cpp
+++ b/src/widgets/ASlider.cpp
@@ -78,6 +78,7 @@ of an LWSlider or ASlider.
 
 #include "../Experimental.h"
 #include "ASlider.h"
+#include "Ruler.h"
 
 #include "../AColor.h"
 #include "../ImageManipulation.h"