diff --git a/default.nix b/default.nix
index c0e28b6..4b12bf6 100644
--- a/default.nix
+++ b/default.nix
@@ -1,7 +1,7 @@
 { mkDerivation, aeson, annotated-exception, async, base, bytestring
-, cereal, containers, directory, ekg-core, hedgehog, hspec
-, hspec-hedgehog, katip, lens, lens-aeson, lib, network, process
-, stm, text, time, unordered-containers, uuid, websockets
+, cereal, containers, directory, ekg-core, filepath, hedgehog
+, hspec, hspec-hedgehog, katip, lens, lens-aeson, lib, network
+, process, stm, text, time, unordered-containers, uuid, websockets
 }:
 mkDerivation {
   pname = "home-assistant-controller";
@@ -11,13 +11,13 @@ mkDerivation {
   isExecutable = true;
   libraryHaskellDepends = [
     aeson annotated-exception async base bytestring cereal containers
-    directory ekg-core katip lens lens-aeson network process stm text
-    time unordered-containers uuid websockets
+    directory ekg-core filepath katip lens lens-aeson network process
+    stm text time unordered-containers uuid websockets
   ];
   executableHaskellDepends = [ base ];
   testHaskellDepends = [
-    aeson annotated-exception async base containers directory ekg-core
-    hedgehog hspec hspec-hedgehog katip process stm text time
+    aeson annotated-exception async base cereal containers directory
+    ekg-core hedgehog hspec hspec-hedgehog katip process stm text time
     unordered-containers uuid
   ];
   license = lib.meta.getLicenseFromSpdxId "BSD-3-Clause";
diff --git a/home-assistant-controller.cabal b/home-assistant-controller.cabal
index 5651e9e..5540196 100644
--- a/home-assistant-controller.cabal
+++ b/home-assistant-controller.cabal
@@ -169,6 +169,7 @@ test-suite home-assistant-controller-test
         hspec,
         stm,
         aeson,
+        cereal,
         text,
         async,
         hedgehog,
diff --git a/src/AFRP.hs b/src/AFRP.hs
index a395b8f..66d0902 100644
--- a/src/AFRP.hs
+++ b/src/AFRP.hs
@@ -390,9 +390,8 @@ data DelayState x a = DelayState
 instance (Serialize x, Serialize a) => Serialize (DelayState x a)
 
 newtype SerializeUTCTime = SerializeUTCTime UTCTime
-  deriving Eq
+  deriving (Eq, Show)
 
--- TODO: Needs '\x -> pure x == get (put x)' test
 instance Serialize SerializeUTCTime where
   put (SerializeUTCTime (UTCTime day time)) = do
     put (toModifiedJulianDay day)
diff --git a/test/AFRPSpec.hs b/test/AFRPSpec.hs
index dd9f567..eaeb4d1 100644
--- a/test/AFRPSpec.hs
+++ b/test/AFRPSpec.hs
@@ -9,9 +9,10 @@ import Data.Foldable (for_)
 import AFRP
 import Data.Functor.Identity (Identity (..))
 import Data.List (sort)
+import Data.Serialize (get, put, runGet, runPut)
 import qualified Data.Set as S
 import qualified Data.Text as T
-import Data.Time (NominalDiffTime, UTCTime (..), utc)
+import Data.Time (Day (..), NominalDiffTime, UTCTime (..), picosecondsToDiffTime, utc)
 import Data.UUID (nil)
 import Hedgehog
 import qualified Hedgehog.Gen as Gen
@@ -86,6 +87,7 @@ spec = describe "AFRP" $ do
   delayEventSpec
   debounceSpec
   rollupSpec
+  serializeSpec
   effSpec
   mapAccumRequestSpec
   preMapAccumRequestSpec
@@ -404,6 +406,20 @@ eventGen = Gen.frequency
   , (1, pure Tick)
   ]
 
+timeGen :: Gen SerializeUTCTime
+timeGen = do
+  day <- ModifiedJulianDay . fromIntegral <$> Gen.int (Range.linear 0 100000)
+  pico <- picosecondsToDiffTime . fromIntegral
+    <$> Gen.int (Range.linear 0 (86400 * 10 ^ (12 :: Int) - 1))
+  pure $ SerializeUTCTime (UTCTime day pico)
+
+serializeSpec :: Spec
+serializeSpec = describe "SerializeUTCTime" $ do
+  it "get (put x) == pure x" $
+    hedgehog $ do
+      x <- forAll timeGen
+      tripping x (runPut . put) (runGet get)
+
 effSpec :: Spec
 effSpec = describe "eff" $ do
   it "lifts a pure effect function into a stateless Mealy" $