diff --git a/byg/src/DependencyGenerator.hs b/byg/src/DependencyGenerator.hs
index 0a6f4d8..4adc8db 100644
--- a/byg/src/DependencyGenerator.hs
+++ b/byg/src/DependencyGenerator.hs
@@ -228,8 +228,11 @@ listDirectory a = runFunctionIO ListDirectory =<< toToken a
 isDirectory :: TokenableTo FilePath a => a -> DepGenM' Bool
 isDirectory a = runFunctionIO IsDirectory =<< toToken a
 
-readTemplate :: TokenableTo FilePath a => a -> DepGenM' Template
-readTemplate a = runFunctionIO ReadTemplate =<< toToken a
+readTemplate :: (TokenableTo FilePath a, TokenableTo Text b) => a -> b -> DepGenM' Template
+readTemplate a b = do
+  a' <- toToken a
+  b' <- toToken b
+  runFunctionIO ReadTemplate $ TupleToken (a', b')
 
 convertImage :: (TokenableTo (FilePath, FilePath) a, TokenableTo ImageConversionSettings b) => a -> b -> DepGenM ()
 convertImage a b = do
diff --git a/byg/src/Evaluation/FunctionIO.hs b/byg/src/Evaluation/FunctionIO.hs
index c478c96..b56a9ce 100644
--- a/byg/src/Evaluation/FunctionIO.hs
+++ b/byg/src/Evaluation/FunctionIO.hs
@@ -24,10 +24,9 @@ evalFunctionIO f x = case (f, x) of
   (IsDirectory, String (StringWrapper s)) ->
     Bool <$> doesDirectoryExist s
 
-  (ReadTemplate, String (StringWrapper s)) -> do
+  (ReadTemplate, Tuple (String (StringWrapper s), Text c)) -> do
     t <- T.readFile s
-    let c = "CONTENT"
-        (beforeContent, after) = T.breakOn c t
+    let (beforeContent, after) = T.breakOn c t
         afterContent = T.drop (T.length c) after
     pure $ Template $ TemplateParts beforeContent afterContent
 
@@ -62,4 +61,4 @@ evalFunctionIO f x = case (f, x) of
     pure $ Text $ TL.toStrict $ B.renderHtml html
 
   _ ->
-    error "unexpected combination of function and argument type"
+    error ("unexpected combination of function and argument type; got function " ++ show f ++ " with argument " ++ show x)
diff --git a/byg/src/SiteGenerator.hs b/byg/src/SiteGenerator.hs
index 6edd2bd..258b828 100644
--- a/byg/src/SiteGenerator.hs
+++ b/byg/src/SiteGenerator.hs
@@ -62,7 +62,7 @@ generateSite = do
   recipesDir <- inject "retter"
   outputRecipesDir <- joinPaths outputDir recipesDir
   makeDir outputRecipesDir
-  template <- readTemplate $ inject "template.html"
+  template <- readTemplate (inject "template.html") (inject "CONTENT")
   indexName <- inject "index.html"
   dirNames <- listDirectory recipesDir
   dirPaths <- mapDepGenM (joinPaths recipesDir) dirNames