diff --git a/core/src/main/java/com/google/bitcoin/protocols/channels/PaymentChannelClientState.java b/core/src/main/java/com/google/bitcoin/protocols/channels/PaymentChannelClientState.java
index bd72eae6..4b3ada8b 100644
--- a/core/src/main/java/com/google/bitcoin/protocols/channels/PaymentChannelClientState.java
+++ b/core/src/main/java/com/google/bitcoin/protocols/channels/PaymentChannelClientState.java
@@ -376,6 +376,7 @@ public class PaymentChannelClientState {
     @VisibleForTesting synchronized void doStoreChannelInWallet(Sha256Hash id) {
         StoredPaymentChannelClientStates channels = (StoredPaymentChannelClientStates)
                 wallet.getExtensions().get(StoredPaymentChannelClientStates.EXTENSION_ID);
+		checkNotNull(channels, "You have not added the StoredPaymentChannelClientStates extension to the wallet.");
         checkState(channels.getChannel(id, multisigContract.getHash()) == null);
         storedChannel = new StoredClientChannel(id, multisigContract, refundTx, myKey, valueToMe, refundFees, true);
         channels.putChannel(storedChannel);