diff --git a/lib/markdown.coffee b/lib/markdown.coffee
index 0277668..6af7759 100644
--- a/lib/markdown.coffee
+++ b/lib/markdown.coffee
@@ -29,6 +29,7 @@ markdown = (text) ->
     return ""
   if typeof text is Function
     text = text()
+  text = text.toString()
   return marked(normaliseTabs(text), {
     smartypants: true
   })