diff --git a/eclair-core/src/test/scala/fr/acinq/eclair/crypto/SphinxSpec.scala b/eclair-core/src/test/scala/fr/acinq/eclair/crypto/SphinxSpec.scala
index 8e7a75e437..da5225800c 100644
--- a/eclair-core/src/test/scala/fr/acinq/eclair/crypto/SphinxSpec.scala
+++ b/eclair-core/src/test/scala/fr/acinq/eclair/crypto/SphinxSpec.scala
@@ -22,8 +22,7 @@ import fr.acinq.eclair.crypto.Sphinx.RouteBlinding.{BlindedRoute, BlindedRouteDe
 import fr.acinq.eclair.wire.protocol
 import fr.acinq.eclair.wire.protocol._
 import fr.acinq.eclair.{BlockHeight, CltvExpiry, CltvExpiryDelta, MilliSatoshiLong, ShortChannelId, UInt64, randomBytes, randomKey}
-import fr.acinq.eclair.{CltvExpiry, CltvExpiryDelta, MilliSatoshiLong, ShortChannelId, UInt64, randomBytes, randomKey}
-import org.json4s.JsonAST._
+import org.json4s.DefaultFormats
 import org.json4s.jackson.JsonMethods
 import org.scalatest.funsuite.AnyFunSuite
 import scodec.bits._
@@ -453,22 +452,22 @@ class SphinxSpec extends AnyFunSuite {
     assert(decryptionError == expected)
   }
 
+  case class TestVector(encodedFailureMessage: String, hops: Seq[TestHop])
+  case class TestHop(sharedSecret: String, encryptedMessage: String)
+  implicit val formats: DefaultFormats.type = DefaultFormats
+
   test("attributable error test vector") {
     val src = Source.fromFile(new File(getClass.getResource(s"/attributable_error.json").getFile))
-    try {
-      val testVector = JsonMethods.parse(src.mkString).asInstanceOf[JObject].values
-      val encodedFailureMessage = ByteVector.fromValidHex(testVector("encodedFailureMessage").asInstanceOf[String])
-      val expected = FailureMessageCodecs.failureOnionPayload(0).decode(encodedFailureMessage.bits).require.value
-      val hops = testVector("hops").asInstanceOf[List[Map[String, String]]]
-      val sharedSecrets = hops.map(hop => ByteVector32(ByteVector.fromValidHex(hop("sharedSecret")))).reverse
-      val encryptedMessage = hops.map(hop => ByteVector.fromValidHex(hop("encryptedMessage"))).last
-      val nodeIds = (1 to 5).map(_ => randomKey().publicKey)
-      val Right(DecryptedFailurePacket(originNode, failureMessage)) = AttributableErrorPacket.decrypt(encryptedMessage, sharedSecrets.zip(nodeIds))
-      assert(originNode == nodeIds.last)
-      assert(failureMessage == expected)
-    } finally {
-      src.close()
-    }
+    val testVector = JsonMethods.parse(src.mkString).extract[TestVector]
+    src.close()
+    val encodedFailureMessage = ByteVector.fromValidHex(testVector.encodedFailureMessage)
+    val expected = FailureMessageCodecs.failureOnionPayload(0).decode(encodedFailureMessage.bits).require.value
+    val sharedSecrets = testVector.hops.map(hop => ByteVector32(ByteVector.fromValidHex(hop.sharedSecret))).reverse
+    val encryptedMessage = testVector.hops.map(hop => ByteVector.fromValidHex(hop.encryptedMessage)).last
+    val nodeIds = (1 to testVector.hops.length).map(_ => randomKey().publicKey)
+    val Right(DecryptedFailurePacket(originNode, failureMessage)) = AttributableErrorPacket.decrypt(encryptedMessage, sharedSecrets.zip(nodeIds))
+    assert(originNode == nodeIds.last)
+    assert(failureMessage == expected)
   }
 
   test("create blinded route (reference test vector)") {