diff --git a/mercurial/templates/static/style-paper.css b/mercurial/templates/static/style-paper.css
--- a/mercurial/templates/static/style-paper.css
+++ b/mercurial/templates/static/style-paper.css
@@ -218,6 +218,7 @@ h3 {
   display: inline-block;
   width: 100%;
   padding: 1px 0px;
+  white-space: pre-wrap;
   counter-increment: lineno;
 }