3 files changed, 35 insertions, 4 deletions
diff --git a/src/Hakyll/Core/Compiler/Internal.hs b/src/Hakyll/Core/Compiler/Internal.hs
index fbb7528..5b3e466 100644
--- a/src/Hakyll/Core/Compiler/Internal.hs
+++ b/src/Hakyll/Core/Compiler/Internal.hs
@@ -1,9 +1,9 @@
 --------------------------------------------------------------------------------
 -- | Internally used compiler module
+{-# LANGUAGE FlexibleInstances          #-}
 {-# LANGUAGE GADTs                      #-}
 {-# LANGUAGE GeneralizedNewtypeDeriving #-}
-{-# LANGUAGE FlexibleInstances #-}
-{-# LANGUAGE MultiParamTypeClasses #-}
+{-# LANGUAGE MultiParamTypeClasses      #-}
 module Hakyll.Core.Compiler.Internal
     ( -- * Types
       CompilerRead (..)
@@ -31,7 +31,7 @@ import           Control.Applicative            (Alternative (..),
                                                  Applicative (..), (<$>))
 import           Control.Exception              (SomeException, handle)
 import           Control.Monad                  (forM_)
-import           Control.Monad.Error
+import           Control.Monad.Error            (MonadError (..))
 import           Data.Monoid                    (Monoid (..))
 import           Data.Set                       (Set)
 import qualified Data.Set                       as S
@@ -149,6 +149,7 @@ instance MonadMetadata Compiler where
     getMetadata = compilerGetMetadata
     getMatches  = compilerGetMatches
 
+
 --------------------------------------------------------------------------------
 instance MonadError [String] Compiler where
   throwError = compilerThrow
diff --git a/src/Hakyll/Core/Provider/Metadata.hs b/src/Hakyll/Core/Provider/Metadata.hs
index 0d94ad7..fe2857a 100644
--- a/src/Hakyll/Core/Provider/Metadata.hs
+++ b/src/Hakyll/Core/Provider/Metadata.hs
@@ -4,6 +4,9 @@ module Hakyll.Core.Provider.Metadata
     ( loadMetadata
     , metadata
     , page
+
+      -- This parser can be reused in some places
+    , metadataKey
     ) where
 
 
@@ -23,6 +26,7 @@ import           Text.Parsec.String            (Parser)
 import           Hakyll.Core.Identifier
 import           Hakyll.Core.Metadata
 import           Hakyll.Core.Provider.Internal
+import           Hakyll.Core.Util.Parser
 import           Hakyll.Core.Util.String
 
 
@@ -93,7 +97,8 @@ newline = P.string "\n" <|> P.string "\r\n"
 -- | Parse a single metadata field
 metadataField :: Parser (String, String)
 metadataField = do
-    key <- P.manyTill P.alphaNum $ P.char ':'
+    key <- metadataKey
+    _   <- P.char ':'
     P.skipMany1 inlineSpace <?> "space followed by metadata for: " ++ key
     value     <- P.manyTill P.anyChar newline
     trailing' <- P.many trailing
diff --git a/src/Hakyll/Core/Util/Parser.hs b/src/Hakyll/Core/Util/Parser.hs
new file mode 100644
index 0000000..afa72c1
--- /dev/null
+++ b/src/Hakyll/Core/Util/Parser.hs
@@ -0,0 +1,25 @@
+--------------------------------------------------------------------------------
+-- | Parser utilities
+module Hakyll.Core.Util.Parser
+    ( metadataKey
+    , reservedKeys
+    ) where
+
+
+--------------------------------------------------------------------------------
+import           Control.Applicative ((<$>), (<*>), (<|>))
+import           Control.Monad       (mzero)
+import qualified Text.Parsec         as P
+import           Text.Parsec.String  (Parser)
+
+
+--------------------------------------------------------------------------------
+metadataKey :: Parser String
+metadataKey = do
+    i <- (:) <$> P.letter <*> (P.many $ P.alphaNum <|> P.oneOf " _-.")
+    if i `elem` reservedKeys then mzero else return i
+
+
+--------------------------------------------------------------------------------
+reservedKeys :: [String]
+reservedKeys = ["if", "else","endif"]