diff --git a/contracts/src/main/kotlin/com/r3corda/contracts/IRS.kt b/contracts/src/main/kotlin/com/r3corda/contracts/IRS.kt
index 65b4ff6fea..e55d9682d4 100644
--- a/contracts/src/main/kotlin/com/r3corda/contracts/IRS.kt
+++ b/contracts/src/main/kotlin/com/r3corda/contracts/IRS.kt
@@ -672,8 +672,8 @@ class InterestRateSwap() : ClauseVerifier() {
             return (fixedLeg.fixedRatePayer.owningKey in ourKeys) || (floatingLeg.floatingRatePayer.owningKey in ourKeys)
         }
 
-        override val parties: Array<Party>
-            get() = arrayOf(fixedLeg.fixedRatePayer, floatingLeg.floatingRatePayer)
+        override val parties: List<Party>
+            get() = listOf(fixedLeg.fixedRatePayer, floatingLeg.floatingRatePayer)
 
         override fun nextScheduledActivity(thisStateRef: StateRef, protocolLogicRefFactory: ProtocolLogicRefFactory): ScheduledActivity? {
             val nextFixingOf = nextFixingOf() ?: return null
diff --git a/core/src/main/kotlin/com/r3corda/core/contracts/Structures.kt b/core/src/main/kotlin/com/r3corda/core/contracts/Structures.kt
index bfa70fdaa0..9815225118 100644
--- a/core/src/main/kotlin/com/r3corda/core/contracts/Structures.kt
+++ b/core/src/main/kotlin/com/r3corda/core/contracts/Structures.kt
@@ -230,7 +230,7 @@ interface DealState : LinearState {
     val ref: String
 
     /** Exposes the Parties involved in a generic way */
-    val parties: Array<Party>
+    val parties: List<Party>
 
     // TODO: This works by editing the keys used by a Party which is invalid.
     fun withPublicKey(before: Party, after: PublicKey): DealState