diff --git a/packages/arb-avm-cpp/cmachine/arbcore.go b/packages/arb-avm-cpp/cmachine/arbcore.go
index 866244a239..b62b30b8c6 100644
--- a/packages/arb-avm-cpp/cmachine/arbcore.go
+++ b/packages/arb-avm-cpp/cmachine/arbcore.go
@@ -90,28 +90,24 @@ func (ac *ArbCore) PrintCoreThreadBacktrace() {
 	C.arbCorePrintCoreThreadBacktrace(ac.c)
 }
 
+// Note: the slices field of the returned struct needs manually freed by C.free
 func sequencerBatchItemsToByteSliceArray(batchItems []inbox.SequencerBatchItem) C.struct_ByteSliceArrayStruct {
 	return bytesArrayToByteSliceArray(encodeSequencerBatchItems(batchItems))
 }
 
+// Note: the slices field of the returned struct needs manually freed by C.free
 func delayedMessagesToByteSliceArray(delayedMessages []inbox.DelayedMessage) C.struct_ByteSliceArrayStruct {
 	return bytesArrayToByteSliceArray(encodeDelayedMessages(delayedMessages))
 }
 
-func u256ArrayToByteSliceArray(nums []*big.Int) C.struct_ByteSliceArrayStruct {
-	var data [][]byte
-	for _, num := range nums {
-		data = append(data, math.U256Bytes(num))
-	}
-	return bytesArrayToByteSliceArray(data)
-}
-
 func (ac *ArbCore) DeliverMessages(previousMessageCount *big.Int, previousSeqBatchAcc common.Hash, seqBatchItems []inbox.SequencerBatchItem, delayedMessages []inbox.DelayedMessage, reorgSeqBatchItemCount *big.Int) bool {
 	defer runtime.KeepAlive(ac)
 	previousMessageCountPtr := unsafeDataPointer(math.U256Bytes(previousMessageCount))
 	previousSeqBatchAccPtr := unsafeDataPointer(previousSeqBatchAcc.Bytes())
 	seqBatchItemsSlice := sequencerBatchItemsToByteSliceArray(seqBatchItems)
+	defer C.free(seqBatchItemsSlice.slices)
 	delayedMessagesSlice := delayedMessagesToByteSliceArray(delayedMessages)
+	defer C.free(delayedMessagesSlice.slices)
 
 	var cReorgSeqBatchItemCount unsafe.Pointer
 	if reorgSeqBatchItemCount != nil {
diff --git a/packages/arb-avm-cpp/cmachine/machine.go b/packages/arb-avm-cpp/cmachine/machine.go
index 9752ed3505..d5d26acf40 100644
--- a/packages/arb-avm-cpp/cmachine/machine.go
+++ b/packages/arb-avm-cpp/cmachine/machine.go
@@ -171,6 +171,7 @@ func (m *Machine) ExecuteAssertion(
 	)
 }
 
+// Note: the slices field of the returned struct needs manually freed by C.free
 func bytesArrayToByteSliceArray(bytes [][]byte) C.struct_ByteSliceArrayStruct {
 	byteSlices := encodeByteSliceList(bytes)
 	sliceArrayData := C.malloc(C.size_t(C.sizeof_struct_ByteSliceStruct * len(byteSlices)))
@@ -190,6 +191,7 @@ func (m *Machine) ExecuteAssertionAdvanced(
 ) (*protocol.ExecutionAssertion, []value.Value, uint64, error) {
 	defer runtime.KeepAlive(m)
 	conf := C.machineExecutionConfigCreate()
+	defer C.machineExecutionConfigDestroy(conf)
 
 	C.machineExecutionConfigSetMaxGas(conf, C.uint64_t(maxGas), boolToCInt(goOverGas))
 
@@ -197,8 +199,6 @@ func (m *Machine) ExecuteAssertionAdvanced(
 	defer C.free(msgData.slices)
 	C.machineExecutionConfigSetInboxMessages(conf, msgData)
 
-	C.machineExecutionConfigSetInboxMessages(conf, msgData)
-
 	sideloadsData := bytesArrayToByteSliceArray(encodeInboxMessages(sideloads))
 	defer C.free(sideloadsData.slices)
 	C.machineExecutionConfigSetSideloads(conf, sideloadsData)