1 files changed, 3 insertions, 2 deletions

diff --git a/spec/src/Thermoprint/API.hs b/spec/src/Thermoprint/API.hs
index 00115f3..e3d4b61 100644
--- a/spec/src/Thermoprint/API.hs
+++ b/spec/src/Thermoprint/API.hs
@@ -30,12 +30,13 @@ import qualified Data.IntMap.Strict as IntMap (foldMapWithKey, singleton)
 
 import Data.Text (Text)
 
+import Data.Typeable (Typeable)
 import GHC.Generics (Generic)
+import Control.DeepSeq (NFData)
 
 import Data.Proxy (Proxy(..))
 
 import Control.Exception (Exception)
-import Data.Typeable (Typeable)
 
 instance (Integral k, Ord k, ToJSON v) => ToJSON (Map k v) where
   toJSON = toJSON . Map.foldMapWithKey (IntMap.singleton . castId)
@@ -55,7 +56,7 @@ data JobStatus = Queued PrinterId
                deriving (Generic, Show, Read, FromJSON, ToJSON)
 
 data PrintingError = UnknownError
-                   deriving (Typeable, Generic, Show, Read, FromJSON, ToJSON, Exception)
+                   deriving (Typeable, Generic, NFData, Show, Read, FromJSON, ToJSON, Exception)
 
 type DraftTitle = Text