diff --git a/scalus-cardano-ledger/shared/src/main/scala/scalus/cardano/txbuilder/TransactionBuilder.scala b/scalus-cardano-ledger/shared/src/main/scala/scalus/cardano/txbuilder/TransactionBuilder.scala
index 045cee36a..1d9da02e7 100644
--- a/scalus-cardano-ledger/shared/src/main/scala/scalus/cardano/txbuilder/TransactionBuilder.scala
+++ b/scalus-cardano-ledger/shared/src/main/scala/scalus/cardano/txbuilder/TransactionBuilder.scala
@@ -340,15 +340,17 @@ object TransactionBuilder {
         /** Conversion help to Scalus [[scalus.cardano.ledger.Utxos]] */
         def getUtxos: Utxos = this.resolvedUtxos.utxos
 
-        /** Validate a context according so a set of ledger rules */
+        /** Validate a context according to a set of ledger rules */
         def validate(
             validators: Seq[Validator],
-            protocolParams: ProtocolParams
+            protocolParams: ProtocolParams,
+            validationSlot: Long,
         ): Either[TransactionException, Context] = {
+            // FIXME: this should either be passed explicitly as "validationCertState" or built in the builder context
             val certState = CertState.empty
             val context = SContext(
               this.transaction.body.value.fee,
-              UtxoEnv(1L, protocolParams, certState, network)
+              UtxoEnv(validationSlot, protocolParams, certState, network)
             )
             val state = SState(this.getUtxos, certState)
             validators
@@ -363,6 +365,7 @@ object TransactionBuilder {
         def finalizeContext(
             protocolParams: ProtocolParams,
             diffHandler: DiffHandler,
+            validationSlot: Long,
             evaluator: PlutusScriptEvaluator,
             validators: Seq[Validator]
         ): Either[SomeBuildError, Context] = {
@@ -393,7 +396,7 @@ object TransactionBuilder {
                     .map(BalancingError(_, this))
 
                 validatedCtx <- balancedCtx
-                    .validate(validators, protocolParams)
+                    .validate(validators, protocolParams, validationSlot)
                     .left
                     .map(ValidationError(_, this))
 
diff --git a/scalus-cardano-ledger/shared/src/main/scala/scalus/cardano/txbuilder/TxBuilder.scala b/scalus-cardano-ledger/shared/src/main/scala/scalus/cardano/txbuilder/TxBuilder.scala
index 3862c662a..fdd4d0878 100644
--- a/scalus-cardano-ledger/shared/src/main/scala/scalus/cardano/txbuilder/TxBuilder.scala
+++ b/scalus-cardano-ledger/shared/src/main/scala/scalus/cardano/txbuilder/TxBuilder.scala
@@ -931,12 +931,14 @@ case class TxBuilder(
       *
       * @param diffHandler
       *   the handler for managing transaction balance differences (change)
+      * @param validationSlot
+      *   the slot against which the ledger rules are validated. Defaults to 0
       * @return
       *   a new TxBuilder with the finalized transaction
       * @throws RuntimeException
       *   if script execution fails or if the transaction cannot be balanced
       */
-    def build(diffHandler: DiffHandler): TxBuilder = {
+    def build(diffHandler: DiffHandler, validationSlot: Long): TxBuilder = {
         val network = env.network
         val params = env.protocolParams
         // Could be a good idea to immediately `modify` on every step, maybe not tho.
@@ -948,6 +950,7 @@ case class TxBuilder(
             finalized <- withAttachments.finalizeContext(
               params,
               diffHandler,
+              validationSlot,
               evaluator,
               validators
             )
@@ -969,14 +972,17 @@ case class TxBuilder(
       *
       * @param changeTo
       *   the address to receive any remaining value (change)
+      * @param validationSlot
+      *   the slot against which the ledger rules are validated. Defaults to 0.
       * @return
       *   a new TxBuilder with the finalized transaction
       * @throws RuntimeException
       *   if script execution fails or if the transaction cannot be balanced
       */
-    def build(changeTo: Address): TxBuilder = {
-        build(diffHandler =
-            (diff, tx) => Change.handleChange(diff, tx, changeTo, env.protocolParams)
+    def build(changeTo: Address, validationSlot: Long = 1): TxBuilder = {
+        build(
+          diffHandler = (diff, tx) => Change.handleChange(diff, tx, changeTo, env.protocolParams),
+          validationSlot = validationSlot
         )
     }
 
@@ -1105,7 +1111,8 @@ case class TxBuilder(
     private def completeLoop(
         pool: UtxoPool,
         sponsor: Address,
-        maxIterations: Int
+        maxIterations: Int,
+        validationSlot: Long = 1
     ): TxBuilder = {
         if maxIterations <= 0 then {
             throw new RuntimeException(
@@ -1136,6 +1143,7 @@ case class TxBuilder(
                 ctxWithAttachments.finalizeContext(
                   env.protocolParams,
                   diffHandler,
+                  validationSlot,
                   evaluator,
                   validators
                 ) match {