diff --git a/plutus-core/changelog.d/20240517_094957_unsafeFixIO_v2_new_prims.md b/plutus-core/changelog.d/20240517_094957_unsafeFixIO_v2_new_prims.md
new file mode 100644
index 00000000000..1cd71254e72
--- /dev/null
+++ b/plutus-core/changelog.d/20240517_094957_unsafeFixIO_v2_new_prims.md
@@ -0,0 +1,5 @@
+
+### Added
+
+- Primitives `integerToByteString` and `byteStringToInteger` are added to PlutusV2,
+  enabled at protocol version 10.
diff --git a/plutus-ledger-api/src/PlutusLedgerApi/Common/ProtocolVersions.hs b/plutus-ledger-api/src/PlutusLedgerApi/Common/ProtocolVersions.hs
index fdf7fbc08a5..158c57fde4a 100644
--- a/plutus-ledger-api/src/PlutusLedgerApi/Common/ProtocolVersions.hs
+++ b/plutus-ledger-api/src/PlutusLedgerApi/Common/ProtocolVersions.hs
@@ -11,6 +11,7 @@ module PlutusLedgerApi.Common.ProtocolVersions
     , vasilPV
     , valentinePV
     , conwayPV
+    , conwayPlus1PV
     , knownPVs
     , futurePV
     ) where
@@ -68,10 +69,25 @@ valentinePV = MajorProtocolVersion 8
 conwayPV :: MajorProtocolVersion
 conwayPV = MajorProtocolVersion 9
 
+-- | The next HF after Conway. It doesn't yet have a name, and it's not
+-- yet known whether it will be an intra-era HF or introduce a new era.
+conwayPlus1PV :: MajorProtocolVersion
+conwayPlus1PV = MajorProtocolVersion 10
+
 -- | The set of protocol versions that are "known", i.e. that have been released
 -- and have actual differences associated with them.
 knownPVs :: Set.Set MajorProtocolVersion
-knownPVs = Set.fromList [ shelleyPV, allegraPV, maryPV, alonzoPV, vasilPV, valentinePV, conwayPV ]
+knownPVs =
+  Set.fromList
+    [ shelleyPV
+    , allegraPV
+    , maryPV
+    , alonzoPV
+    , vasilPV
+    , valentinePV
+    , conwayPV
+    , conwayPlus1PV
+    ]
 
 -- | This is a placeholder for when we don't yet know what protocol version will
 -- be used for something. It's a very high protocol version that should never
diff --git a/plutus-ledger-api/src/PlutusLedgerApi/Common/Versions.hs b/plutus-ledger-api/src/PlutusLedgerApi/Common/Versions.hs
index 728b096ea3c..24a553dd651 100644
--- a/plutus-ledger-api/src/PlutusLedgerApi/Common/Versions.hs
+++ b/plutus-ledger-api/src/PlutusLedgerApi/Common/Versions.hs
@@ -81,7 +81,6 @@ instance Pretty PlutusLedgerLanguage where
     pretty = viaShow
 
 {-| A map indicating which builtin functions were introduced in which 'MajorProtocolVersion'.
-Each builtin function should appear at most once.
 
 This __must__ be updated when new builtins are added.
 See Note [New builtins/language versions and protocol versions]
@@ -107,6 +106,9 @@ builtinsIntroducedIn = Map.fromList [
   ((PlutusV2, valentinePV), Set.fromList [
           VerifyEcdsaSecp256k1Signature, VerifySchnorrSecp256k1Signature
           ]),
+  ((PlutusV2, conwayPlus1PV), Set.fromList [
+          IntegerToByteString, ByteStringToInteger
+          ]),
   ((PlutusV3, conwayPV), Set.fromList [
           Bls12_381_G1_add, Bls12_381_G1_neg, Bls12_381_G1_scalarMul,
           Bls12_381_G1_equal, Bls12_381_G1_hashToGroup,
@@ -173,10 +175,10 @@ and 'MajorProtocolVersion'?
 See Note [New builtins/language versions and protocol versions]
 -}
 builtinsAvailableIn :: PlutusLedgerLanguage -> MajorProtocolVersion -> Set.Set DefaultFun
-builtinsAvailableIn thisLv thisPv = fold $ Map.elems $
-    Map.takeWhileAntitone builtinAvailableIn builtinsIntroducedIn
+builtinsAvailableIn thisLv thisPv = fold $
+    Map.filterWithKey (const . alreadyIntroduced) builtinsIntroducedIn
     where
-      builtinAvailableIn :: (PlutusLedgerLanguage, MajorProtocolVersion) -> Bool
-      builtinAvailableIn (introducedInLv,introducedInPv) =
+      alreadyIntroduced :: (PlutusLedgerLanguage, MajorProtocolVersion) -> Bool
+      alreadyIntroduced (introducedInLv,introducedInPv) =
           -- both should be satisfied
           introducedInLv <= thisLv && introducedInPv <= thisPv