diff --git a/src/FsSpectre/Widgets/PanelBuilder.fs b/src/FsSpectre/Widgets/PanelBuilder.fs
index 27e7004..d0c95eb 100644
--- a/src/FsSpectre/Widgets/PanelBuilder.fs
+++ b/src/FsSpectre/Widgets/PanelBuilder.fs
@@ -29,7 +29,7 @@ module PanelBuilder =
             panel.Header <- PanelHeader(text)
             panel
 
-        [<CustomOperation "Expand">]
+        [<CustomOperation "expand">]
         member __.Expand(panel: Panel) =
             panel.Expand <- true
             panel