diff --git a/binary.cabal b/binary.cabal
index 288117ee..199a6cae 100644
--- a/binary.cabal
+++ b/binary.cabal
@@ -67,6 +67,7 @@ test-suite qc
   other-modules:
     Action
     Arbitrary
+    Generic
   build-depends:
     base >= 4.5.0.0 && < 5,
     base-orphans >=0.8.1 && <0.9,
diff --git a/src/Data/Binary/Generic.hs b/src/Data/Binary/Generic.hs
index 89f67f28..c41d8988 100644
--- a/src/Data/Binary/Generic.hs
+++ b/src/Data/Binary/Generic.hs
@@ -83,7 +83,7 @@ instance Binary a => GBinaryGet (K1 i a) where
 -- encode the constructor. If it has 2^16 constructors or less it will
 -- use two bytes, and so on till 2^64-1.
 
-#define GUARD(WORD) (size - 1) <= fromIntegral (maxBound :: WORD)
+#define GUARD(WORD) size <= fromIntegral (maxBound :: WORD)
 #define PUTSUM(WORD) GUARD(WORD) = putSum (0 :: WORD) (fromIntegral size)
 #define GETSUM(WORD) GUARD(WORD) = (get :: Get WORD) >>= checkGetSum (fromIntegral size)
 
diff --git a/tests/Generic.hs b/tests/Generic.hs
new file mode 100644
index 00000000..5694af32
--- /dev/null
+++ b/tests/Generic.hs
@@ -0,0 +1,28 @@
+{-# LANGUAGE DeriveGeneric, DeriveAnyClass #-}
+module Generic where
+
+import           Data.Binary
+import           GHC.Generics
+import           Test.QuickCheck
+
+data Generic256 =
+       C00 | C01 | C02 | C03 | C04 | C05 | C06 | C07 | C08 | C09 | C0a | C0b | C0c | C0d | C0e | C0f
+     | C10 | C11 | C12 | C13 | C14 | C15 | C16 | C17 | C18 | C19 | C1a | C1b | C1c | C1d | C1e | C1f
+     | C20 | C21 | C22 | C23 | C24 | C25 | C26 | C27 | C28 | C29 | C2a | C2b | C2c | C2d | C2e | C2f
+     | C30 | C31 | C32 | C33 | C34 | C35 | C36 | C37 | C38 | C39 | C3a | C3b | C3c | C3d | C3e | C3f
+     | C40 | C41 | C42 | C43 | C44 | C45 | C46 | C47 | C48 | C49 | C4a | C4b | C4c | C4d | C4e | C4f
+     | C50 | C51 | C52 | C53 | C54 | C55 | C56 | C57 | C58 | C59 | C5a | C5b | C5c | C5d | C5e | C5f
+     | C60 | C61 | C62 | C63 | C64 | C65 | C66 | C67 | C68 | C69 | C6a | C6b | C6c | C6d | C6e | C6f
+     | C70 | C71 | C72 | C73 | C74 | C75 | C76 | C77 | C78 | C79 | C7a | C7b | C7c | C7d | C7e | C7f
+     | C80 | C81 | C82 | C83 | C84 | C85 | C86 | C87 | C88 | C89 | C8a | C8b | C8c | C8d | C8e | C8f
+     | C90 | C91 | C92 | C93 | C94 | C95 | C96 | C97 | C98 | C99 | C9a | C9b | C9c | C9d | C9e | C9f
+     | Ca0 | Ca1 | Ca2 | Ca3 | Ca4 | Ca5 | Ca6 | Ca7 | Ca8 | Ca9 | Caa | Cab | Cac | Cad | Cae | Caf
+     | Cb0 | Cb1 | Cb2 | Cb3 | Cb4 | Cb5 | Cb6 | Cb7 | Cb8 | Cb9 | Cba | Cbb | Cbc | Cbd | Cbe | Cbf
+     | Cc0 | Cc1 | Cc2 | Cc3 | Cc4 | Cc5 | Cc6 | Cc7 | Cc8 | Cc9 | Cca | Ccb | Ccc | Ccd | Cce | Ccf
+     | Cd0 | Cd1 | Cd2 | Cd3 | Cd4 | Cd5 | Cd6 | Cd7 | Cd8 | Cd9 | Cda | Cdb | Cdc | Cdd | Cde | Cdf
+     | Ce0 | Ce1 | Ce2 | Ce3 | Ce4 | Ce5 | Ce6 | Ce7 | Ce8 | Ce9 | Cea | Ceb | Cec | Ced | Cee | Cef
+     | Cf0 | Cf1 | Cf2 | Cf3 | Cf4 | Cf5 | Cf6 | Cf7 | Cf8 | Cf9 | Cfa | Cfb | Cfc | Cfd | Cfe | Cff
+  deriving (Eq, Enum, Bounded, Show, Generic, Binary)
+
+instance Arbitrary Generic256 where                                                                                                                                                               
+    arbitrary = oneof (map pure [minBound..maxBound])
diff --git a/tests/QC.hs b/tests/QC.hs
index 776768f4..1bc160fd 100644
--- a/tests/QC.hs
+++ b/tests/QC.hs
@@ -40,6 +40,7 @@ import           Test.QuickCheck hiding (total)
 
 import qualified Action                               (tests)
 import           Arbitrary                            ()
+import           Generic                              (Generic256)
 import           Data.Binary
 import           Data.Binary.Get
 import           Data.Binary.Put
@@ -528,6 +529,11 @@ prop_fixed_resolution_constr x = runGet get (runPut (fixedPut x)) == x
 
 ------------------------------------------------------------------------
 
+prop_Generic256 :: Generic256 -> Property
+prop_Generic256 = roundTripWith put get
+
+------------------------------------------------------------------------
+
 type T a = a -> Property
 type B a = a -> Bool
 
@@ -708,4 +714,6 @@ tests =
             ]
 #endif
         , testTypeable
+        , testGroup "Generic"
+            [ testProperty "Generic256" $ p prop_Generic256 ]
         ]