Fixed obscure issue with Hakyll? See Hakyll FAQ

https://jaspervdj.be/hakyll/tutorials/faq.html#hgetcontents-invalid-argument-or-commitbuffer-invalid-argument

site.hs

@@ -10,6 +10,7 @@ Portability : POSIX
 import           Data.Monoid (mappend)
 import           Hakyll
 import           System.FilePath
+import qualified GHC.IO.Encoding as E
 
 -- | Configuration for the RSS and ATOM feeds.
 feedConfiguration :: FeedConfiguration
@@ -23,7 +24,9 @@ feedConfiguration = FeedConfiguration
 
 -- | Main entry point for generating all code via Hakyll
 main :: IO ()
-main = hakyll $ do
+main = do
+  E.setLocaleEncoding E.utf8
+  hakyll $ do
     -- Build up tags
     tags <- buildTags "posts/*" (fromCapture "tags/*.html")
     let postCtxTags = postCtxWithTags tags