diff --git a/core/wiki/functions/themes.tid b/core/wiki/functions/themes.tid
index 2abcca962..66841d07f 100644
--- a/core/wiki/functions/themes.tid
+++ b/core/wiki/functions/themes.tid
@@ -108,7 +108,7 @@ code-body: yes
 
 \function get.current.theme() [{$:/theme}!is[blank]] :else[all[tiddlers+shadows]plugin-type[theme]plugin-priority[0]first[]]
 
-\function get.theme.storywidthoverlap() [[sqrt(pow(]addsuffix<get.theme.metric storyright>addsuffix[ - ]addsuffix<get.theme.metric storywidth>addsuffix[ - ]addsuffix<get.theme.metric storyleft>addsuffix[,2))]]
+\function get.theme.storywidthoverlap() [[max((]addsuffix<get.theme.metric storyright>addsuffix[ - ]addsuffix<get.theme.metric storywidth>addsuffix[ - ]addsuffix<get.theme.metric storyleft>addsuffix[),(-1 * (]addsuffix<get.theme.metric storyright>addsuffix[ - ]addsuffix<get.theme.metric storywidth>addsuffix[ - ]addsuffix<get.theme.metric storyleft>addsuffix[)))]]
 
 \function get.theme.storyleftpadding.excess() [[calc(]addsuffix<get.theme.metric storypaddingleft>addsuffix[ - ]addsuffix<get.story-sidebar.overlap>addsuffix[)]]