diff --git a/app/Foliage/Meta.hs b/app/Foliage/Meta.hs
index b5642d8..5f6c91d 100644
--- a/app/Foliage/Meta.hs
+++ b/app/Foliage/Meta.hs
@@ -32,6 +32,8 @@ where
 
 import Control.Applicative ((<|>))
 import Control.Monad (void)
+import Control.Monad.State (modify)
+import Data.HashMap.Strict qualified as HashMap
 import Data.List (sortOn)
 import Data.Maybe (fromMaybe)
 import Data.Ord (Down (Down))
@@ -121,10 +123,25 @@ data PackageVersionSpec = PackageVersionSpec
   deriving (Show, Eq, Generic)
   deriving anyclass (Binary, Hashable, NFData)
 
+matchMaybe :: forall a. Toml.TomlBiMap a Toml.AnyValue -> Toml.Key -> TomlCodec (Maybe a)
+matchMaybe bimap@(Toml.BiMap {}) key = Toml.Codec input output
+  where
+    input :: Toml.TomlEnv (Maybe a)
+    input toml = case HashMap.lookup key (Toml.tomlPairs toml) of
+      Nothing -> pure Nothing
+      Just anyVal -> pure <$> Toml.whenLeftBiMapError key (Toml.backward bimap anyVal) pure
+
+    output :: Maybe a -> Toml.TomlState (Maybe a)
+    output Nothing = pure Nothing
+    output (Just a) = do
+      anyVal <- Toml.eitherToTomlState $ Toml.forward bimap a
+      Just a <$ modify (Toml.insertKeyAnyVal key anyVal)
+
 sourceMetaCodec :: TomlCodec PackageVersionSpec
 sourceMetaCodec =
   PackageVersionSpec
-    <$> Toml.dioptional (timeCodec "timestamp")
+    -- TODO: unsure how to initialize Toml.BiMap ... with Toml._ZonedTime?
+    <$> matchMaybe Toml.BiMap {} "timestamp"
     .= packageVersionTimestamp
     <*> packageSourceCodec
     .= packageVersionSource
diff --git a/foliage.cabal b/foliage.cabal
index 8c45823..48641a7 100644
--- a/foliage.cabal
+++ b/foliage.cabal
@@ -58,6 +58,7 @@ executable foliage
         ed25519,
         filepath             >=1.4.2.1    && <1.5,
         hackage-security     >=0.6.2.1    && <0.7,
+        mtl,
         network-uri         ^>=2.6.4.1,
         optparse-applicative >=0.17.0.0   && <0.18,
         shake                >=0.19.6     && <0.20,
@@ -67,5 +68,6 @@ executable foliage
         time                 >=1.9.3      && <1.13,
         time-compat          >=1.9.6.1    && <1.10,
         tomland              >=1.3.3.1    && <1.4,
+        unordered-containers,
         with-utf8            >=1.0.2.3    && <1.1,
         zlib                 >=0.6.2.3    && <0.7