diff --git a/core/src/main/kotlin/net/corda/core/internal/InternalUtils.kt b/core/src/main/kotlin/net/corda/core/internal/InternalUtils.kt
index 4a748251d3..8257623faf 100644
--- a/core/src/main/kotlin/net/corda/core/internal/InternalUtils.kt
+++ b/core/src/main/kotlin/net/corda/core/internal/InternalUtils.kt
@@ -20,14 +20,12 @@ import net.corda.core.cordapp.CordappContext
 import net.corda.core.crypto.*
 import net.corda.core.identity.CordaX500Name
 import net.corda.core.node.ServicesForResolution
-import net.corda.core.serialization.SerializationContext
-import net.corda.core.serialization.SerializedBytes
-import net.corda.core.serialization.deserialize
-import net.corda.core.serialization.serialize
+import net.corda.core.serialization.*
 import net.corda.core.transactions.SignedTransaction
 import net.corda.core.transactions.TransactionBuilder
 import net.corda.core.transactions.WireTransaction
 import net.corda.core.utilities.OpaqueBytes
+import net.corda.core.utilities.UntrustworthyData
 import org.bouncycastle.asn1.x500.X500Name
 import org.bouncycastle.asn1.x500.X500NameBuilder
 import org.bouncycastle.asn1.x500.style.BCStyle
@@ -515,4 +513,15 @@ fun <T> Iterable<T>.sumByLong(selector: (T) -> Long): Long = this.map { selector
  */
 internal fun SignedTransaction.pushToLoggingContext() {
     MDC.put("tx_id", id.toString())
-}
\ No newline at end of file
+}
+
+fun <T : Any> SerializedBytes<Any>.checkPayloadIs(type: Class<T>): UntrustworthyData<T> {
+    val payloadData: T = try {
+        val serializer = SerializationDefaults.SERIALIZATION_FACTORY
+        serializer.deserialize(this, type, SerializationDefaults.P2P_CONTEXT)
+    } catch (ex: Exception) {
+        throw IllegalArgumentException("Payload invalid", ex)
+    }
+    return type.castIfPossible(payloadData)?.let { UntrustworthyData(it) }
+            ?: throw IllegalArgumentException("We were expecting a ${type.name} but we instead got a ${payloadData.javaClass.name} ($payloadData)")
+}
diff --git a/core/src/main/kotlin/net/corda/core/utilities/UntrustworthyData.kt b/core/src/main/kotlin/net/corda/core/utilities/UntrustworthyData.kt
index a240dbb662..57a81d9bec 100644
--- a/core/src/main/kotlin/net/corda/core/utilities/UntrustworthyData.kt
+++ b/core/src/main/kotlin/net/corda/core/utilities/UntrustworthyData.kt
@@ -42,14 +42,3 @@ class UntrustworthyData<out T>(@PublishedApi internal val fromUntrustedWorld: T)
 }
 
 inline fun <T, R> UntrustworthyData<T>.unwrap(validator: (T) -> R): R = validator(fromUntrustedWorld)
-
-fun <T : Any> SerializedBytes<Any>.checkPayloadIs(type: Class<T>): UntrustworthyData<T> {
-    val payloadData: T = try {
-        val serializer = SerializationDefaults.SERIALIZATION_FACTORY
-        serializer.deserialize(this, type, SerializationDefaults.P2P_CONTEXT)
-    } catch (ex: Exception) {
-        throw IllegalArgumentException("Payload invalid", ex)
-    }
-    return type.castIfPossible(payloadData)?.let { UntrustworthyData(it) } ?: throw IllegalArgumentException("We were expecting a ${type.name} but we instead got a " +
-            "${payloadData.javaClass.name} ($payloadData)")
-}
diff --git a/node/src/main/kotlin/net/corda/node/services/statemachine/FlowSessionImpl.kt b/node/src/main/kotlin/net/corda/node/services/statemachine/FlowSessionImpl.kt
index 535360032d..8bae2cc972 100644
--- a/node/src/main/kotlin/net/corda/node/services/statemachine/FlowSessionImpl.kt
+++ b/node/src/main/kotlin/net/corda/node/services/statemachine/FlowSessionImpl.kt
@@ -22,7 +22,7 @@ import net.corda.core.serialization.SerializedBytes
 import net.corda.core.serialization.serialize
 import net.corda.core.utilities.NonEmptySet
 import net.corda.core.utilities.UntrustworthyData
-import net.corda.core.utilities.checkPayloadIs
+import net.corda.core.internal.checkPayloadIs
 
 class FlowSessionImpl(
         override val counterparty: Party,