diff --git a/ouroboros-network-protocols/CHANGELOG.md b/ouroboros-network-protocols/CHANGELOG.md
index 25cd3cf2a24..6e2d7736c80 100644
--- a/ouroboros-network-protocols/CHANGELOG.md
+++ b/ouroboros-network-protocols/CHANGELOG.md
@@ -1,5 +1,13 @@
 # Revision history for ouroboros-network-protocols
 
+## next version
+
+### Breaking changes
+
+* Definition of `TxId` has changed, it's now a newtype wrapper for
+  `Codec.CBOR.Term.Term` type, which indicates that `ouroboros-network` does
+  not specify what `TxId` or `Tx` types are.
+
 ## 0.5.0.3 -- 2023-05-26
 
 * `ghc-9.6` compatibility
diff --git a/ouroboros-network-protocols/test-cddl/specs/common.cddl b/ouroboros-network-protocols/test-cddl/specs/common.cddl
index e04d96fab53..0320bd04072 100644
--- a/ouroboros-network-protocols/test-cddl/specs/common.cddl
+++ b/ouroboros-network-protocols/test-cddl/specs/common.cddl
@@ -21,10 +21,11 @@ origin          = []
 blockHeaderHash = [slotNo, int]
 slotNo          = word64
 
-; In `ouroboros-network` we don't know what are tx (and txId), we mock them
-; with `int`s, that's because `ouroboros-network` is polymorphic over them.
-txId         = int
-tx           = int
+; In this spec we don't specify what transaction idenfiers (txId) or
+; transactions (tx) are themselves, `ouroboros-network` is polymorphic over
+; them.
+txId         = any
+tx           = any
 rejectReason = int
 
 word16 = 0..65535
diff --git a/ouroboros-network-protocols/testlib/Ouroboros/Network/Protocol/TxSubmission2/Test.hs b/ouroboros-network-protocols/testlib/Ouroboros/Network/Protocol/TxSubmission2/Test.hs
index e52f910babf..1cce0e2addb 100644
--- a/ouroboros-network-protocols/testlib/Ouroboros/Network/Protocol/TxSubmission2/Test.hs
+++ b/ouroboros-network-protocols/testlib/Ouroboros/Network/Protocol/TxSubmission2/Test.hs
@@ -31,6 +31,7 @@ import           Control.Monad.IOSim
 import           Control.Monad.ST (runST)
 import           Control.Tracer (Tracer (..), nullTracer)
 
+import qualified Codec.CBOR.Term as CBOR
 import           Codec.Serialise (DeserialiseFailure, Serialise)
 import qualified Codec.Serialise as Serialise (decode, encode)
 
@@ -52,6 +53,7 @@ import           Test.Ouroboros.Network.Testing.Utils (prop_codec_cborM,
                      prop_codec_valid_cbor_encoding, splits2, splits3)
 
 import           Test.QuickCheck as QC
+import           Test.QuickCheck.Instances.ByteString ()
 import           Test.Tasty (TestTree, testGroup)
 import           Test.Tasty.QuickCheck (testProperty)
 
@@ -94,8 +96,22 @@ instance ShowProxy Tx where
 txId :: Tx -> TxId
 txId (Tx txid) = txid
 
-newtype TxId = TxId Int
-  deriving (Eq, Ord, Show, Arbitrary, Serialise)
+-- | We use any `CBOR.Term`.  This allows us to use `any` in cddl specs.
+--
+newtype TxId = TxId CBOR.Term
+  deriving (Eq, Ord, Show, Serialise)
+
+instance Arbitrary TxId where
+    arbitrary = oneof [ TxId . CBOR.TInt <$> arbitrary
+                      , TxId . CBOR.TBytes <$> arbitrary
+                      , TxId . CBOR.TBool <$> arbitrary
+                      ]
+    shrink (TxId term) =
+      case term of
+        CBOR.TInt a   -> TxId . CBOR.TInt   <$> shrink a
+        CBOR.TBytes a -> TxId . CBOR.TBytes <$> shrink a
+        CBOR.TBool a  -> TxId . CBOR.TBool  <$> shrink a
+        _             -> []
 
 instance ShowProxy TxId where
     showProxy _ = "TxId"