diff --git a/klaus/utils.py b/klaus/utils.py
index 3820aba..f206b56 100644
--- a/klaus/utils.py
+++ b/klaus/utils.py
@@ -75,11 +75,7 @@
     if render_markup and markup.can_render(filename):
         return markup.render(filename, code)
 
-    try:
-        lexer = get_lexer_for_filename(filename)
-    except ClassNotFound:
-        lexer = guess_lexer(code)
-
+    lexer = get_lexer_for_filename(filename, code)
     return highlight(code, lexer, KlausFormatter())