1 files changed, 5 insertions, 1 deletions

diff --git a/Data/OpenPGP/Util/Base.hs b/Data/OpenPGP/Util/Base.hs
index aaa02c7..ed0e32c 100644
--- a/Data/OpenPGP/Util/Base.hs
+++ b/Data/OpenPGP/Util/Base.hs
@@ -57,7 +57,11 @@ keyParam c k = fromJustMPI $ lookup c (OpenPGP.key k)
  where
     fromJustMPI :: Maybe OpenPGP.MPI -> Integer
     fromJustMPI (Just (OpenPGP.MPI x)) = x
-    fromJustMPI _ = error "Not a Just MPI, Data.OpenPGP.CryptoAPI"
+    fromJustMPI _ =
+        case k of
+            PublicKeyPacket {} -> error $ "Missing "++show c++" field on "++show (key_algorithm k)++" packet."
+            SecretKeyPacket {} -> error $ "Missing "++show c++" field on "++show (symmetric_algorithm k)
+                                            ++" "++show (key_algorithm k)++" packet."
 
 integerBytesize :: Integer -> Int
 integerBytesize i = fromIntegral $ LZ.length (encode (OpenPGP.MPI i)) - 2