diff --git a/inst/rmarkdown/templates/posterdown_html/resources/template.html b/inst/rmarkdown/templates/posterdown_html/resources/template.html
index fafa557..67da69c 100644
--- a/inst/rmarkdown/templates/posterdown_html/resources/template.html
+++ b/inst/rmarkdown/templates/posterdown_html/resources/template.html
@@ -293,6 +293,9 @@
   width: 1em;
 }
 </style>
+$if(custom_css)$
+<link rel="stylesheet" href=$custom_css$>
+$else$$endif$
 </head>
 <body>