diff --git a/src/clipboard.cpp b/src/clipboard.cpp
index 5258a4b7507..8c1a6bd7153 100644
--- a/src/clipboard.cpp
+++ b/src/clipboard.cpp
@@ -105,7 +105,7 @@ public:
 		return wmInf_.info.x11.display;
 	}
 
-	Window window()
+	Window window() const
 	{
 		return wmInf_.info.x11.window;
 	}