Fails to build with -f-bibutils:
https://bugs.gentoo.org/516640
diff --git a/pandoc-citeproc.hs b/pandoc-citeproc.hs
index 7006e02..f72fa41 100644
--- a/pandoc-citeproc.hs
+++ b/pandoc-citeproc.hs
@@ -1 +1,2 @@
+{-# LANGUAGE CPP #-}
 module Main where
@@ -75,2 +76,3 @@ readFormat = go . map toLower
         go "bibtex"   = Just Bibtex
+#ifdef USE_BIBUTILS
         go "ris"      = Just Ris
@@ -87,2 +89,3 @@ readFormat = go . map toLower
         go "yaml"     = Just Yaml
+#endif
         go _          = Nothing
diff --git a/src/Text/CSL/Input/Bibutils.hs b/src/Text/CSL/Input/Bibutils.hs
index 081fa91..49ddbd0 100644
--- a/src/Text/CSL/Input/Bibutils.hs
+++ b/src/Text/CSL/Input/Bibutils.hs
@@ -64,3 +64,3 @@ readBiblioFile f
 #else
-        _           -> error $ "citeproc: Bibliography format not supported.\n" ++
+        _           -> error $ "citeproc: Bibliography format not supported.\n"
 #endif