diff --git a/libsignal-protocol-dotnet-tests/SessionBuilderTest.cs b/libsignal-protocol-dotnet-tests/SessionBuilderTest.cs
index 4ab868e..fbad9ff 100644
--- a/libsignal-protocol-dotnet-tests/SessionBuilderTest.cs
+++ b/libsignal-protocol-dotnet-tests/SessionBuilderTest.cs
@@ -1,4 +1,4 @@
-/** 
+/** 
  * Copyright (C) 2016 langboost
  * 
  * This program is free software: you can redistribute it and/or modify
@@ -25,6 +25,7 @@
 using System;
 using System.Collections.Generic;
 using System.Text;
+using System.Threading.Tasks;
 
 namespace libsignal_test
 {
@@ -46,10 +47,11 @@ public BobDecryptionCallback(SignalProtocolStore bobStore, String originalMessag
                 this.originalMessage = originalMessage;
             }
 
-            public void handlePlaintext(byte[] plaintext)
+            public Task handlePlaintext(byte[] plaintext, uint sessionVersion)
             {
                 Assert.AreEqual(originalMessage, Encoding.UTF8.GetString(plaintext));
                 Assert.IsFalse(bobStore.ContainsSession(ALICE_ADDRESS));
+                return Task.CompletedTask;
             }
         }
 
@@ -87,7 +89,7 @@ public void testBasicPreKeyV3()
             bobStore.StoreSignedPreKey(22, new SignedPreKeyRecord(22, DateUtil.currentTimeMillis(), bobSignedPreKeyPair, bobSignedPreKeySignature));
 
             SessionCipher bobSessionCipher = new SessionCipher(bobStore, ALICE_ADDRESS);
-            byte[] plaintext = bobSessionCipher.decrypt(incomingMessage, new BobDecryptionCallback(bobStore, originalMessage));
+            byte[] plaintext = bobSessionCipher.decrypt(incomingMessage, new BobDecryptionCallback(bobStore, originalMessage)).Result;
 
             Assert.IsTrue(bobStore.ContainsSession(ALICE_ADDRESS));
             Assert.AreEqual((uint)3, bobStore.LoadSession(ALICE_ADDRESS).getSessionState().getSessionVersion());
diff --git a/libsignal-protocol-dotnet/DecryptionCallback.cs b/libsignal-protocol-dotnet/DecryptionCallback.cs
index b72b20d..8c3fce0 100644
--- a/libsignal-protocol-dotnet/DecryptionCallback.cs
+++ b/libsignal-protocol-dotnet/DecryptionCallback.cs
@@ -1,24 +1,25 @@
-/** 
- * Copyright (C) 2016 smndtrl, langboost
- * 
- * This program is free software: you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation, either version 3 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- * 
- * You should have received a copy of the GNU General Public License
- * along with this program.  If not, see <http://www.gnu.org/licenses/>.
- */
-
+using libsignal.state;
+using System.Threading.Tasks;
+/** 
+* Copyright (C) 2016 smndtrl, langboost
+* 
+* This program is free software: you can redistribute it and/or modify
+* it under the terms of the GNU General Public License as published by
+* the Free Software Foundation, either version 3 of the License, or
+* (at your option) any later version.
+*
+* This program is distributed in the hope that it will be useful,
+* but WITHOUT ANY WARRANTY; without even the implied warranty of
+* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+* GNU General Public License for more details.
+* 
+* You should have received a copy of the GNU General Public License
+* along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
 namespace libsignal
 {
     public interface DecryptionCallback
     {
-        void handlePlaintext(byte[] plaintext);
+        Task handlePlaintext(byte[] plaintext, uint sessionVersion);
     }
 }
diff --git a/libsignal-protocol-dotnet/SessionCipher.cs b/libsignal-protocol-dotnet/SessionCipher.cs
index e269093..8a66849 100644
--- a/libsignal-protocol-dotnet/SessionCipher.cs
+++ b/libsignal-protocol-dotnet/SessionCipher.cs
@@ -7,6 +7,7 @@
 using libsignal.state;
 using libsignal.util;
 using Strilanc.Value;
+using System.Threading.Tasks;
 
 namespace libsignal
 {
@@ -117,7 +118,9 @@ public CiphertextMessage encrypt(byte[] paddedMessage)
         /// <exception cref="UntrustedIdentityException">when the <see cref="IdentityKey"/> of the sender is untrusted.</exception>
         public byte[] decrypt(PreKeySignalMessage ciphertext)
         {
-            return decrypt(ciphertext, new NullDecryptionCallback());
+            var tsk = (decrypt(ciphertext, new NullDecryptionCallback()));
+            tsk.Wait();
+            return tsk.Result;
         }
 
         /// <summary>
@@ -137,7 +140,7 @@ public byte[] decrypt(PreKeySignalMessage ciphertext)
         /// 
         /// <exception cref="InvalidKeyException">when the message is formatted incorrectly.</exception>
         /// <exception cref="UntrustedIdentityException">when the <see cref="IdentityKey"/> of the sender is untrusted.</exception>
-        public byte[] decrypt(PreKeySignalMessage ciphertext, DecryptionCallback callback)
+        public Task<byte[]> decrypt(PreKeySignalMessage ciphertext, DecryptionCallback callback)
         {
             lock (SESSION_LOCK)
             {
@@ -147,7 +150,7 @@ public byte[] decrypt(PreKeySignalMessage ciphertext, DecryptionCallback callbac
 
                 identityKeyStore.SaveIdentity(remoteAddress, sessionRecord.getSessionState().getRemoteIdentityKey());
 
-                callback.handlePlaintext(plaintext);
+                callback.handlePlaintext(plaintext, sessionRecord.getSessionState().getSessionVersion()).Wait();
 
                 sessionStore.StoreSession(remoteAddress, sessionRecord);
 
@@ -156,7 +159,7 @@ public byte[] decrypt(PreKeySignalMessage ciphertext, DecryptionCallback callbac
                     preKeyStore.RemovePreKey(unsignedPreKeyId.ForceGetValue());
                 }
 
-                return plaintext;
+                return Task.FromResult(plaintext);
             }
         }
 
@@ -172,7 +175,9 @@ public byte[] decrypt(PreKeySignalMessage ciphertext, DecryptionCallback callbac
         /// <exception cref="NoSessionException">if there is no established session for this contact.</exception>
         public byte[] decrypt(SignalMessage ciphertext)
         {
-            return decrypt(ciphertext, new NullDecryptionCallback());
+            var tsk = decrypt(ciphertext, new NullDecryptionCallback());
+            tsk.Wait();
+            return tsk.Result;
         }
 
         /// <summary>
@@ -189,7 +194,7 @@ public byte[] decrypt(SignalMessage ciphertext)
         /// <exception cref="LegacyMessageException">if the input is a message formatted by a protocol version that is
         /// no longer supported.</exception>
         /// <exception cref="NoSessionException">if there is no established session for this contact.</exception>
-        public byte[] decrypt(SignalMessage ciphertext, DecryptionCallback callback)
+        public Task<byte[]> decrypt(SignalMessage ciphertext, DecryptionCallback callback)
         {
             lock (SESSION_LOCK)
             {
@@ -207,11 +212,11 @@ public byte[] decrypt(SignalMessage ciphertext, DecryptionCallback callback)
                     throw new UntrustedIdentityException(remoteAddress.Name, sessionRecord.getSessionState().getRemoteIdentityKey());
                 }
 
-                callback.handlePlaintext(plaintext);
+                callback.handlePlaintext(plaintext, sessionRecord.getSessionState().getSessionVersion()).Wait();//no async in a lock
 
                 sessionStore.StoreSession(remoteAddress, sessionRecord);
 
-                return plaintext;
+                return Task.FromResult(plaintext);
             }
         }
 
@@ -391,7 +396,7 @@ private byte[] getPlaintext(MessageKeys messageKeys, byte[] cipherText)
         private class NullDecryptionCallback : DecryptionCallback
         {
 
-            public void handlePlaintext(byte[] plaintext) { }
+            public Task handlePlaintext(byte[] plaintext, uint sessionVersion) => Task.CompletedTask;
         }
     }
 }
diff --git a/libsignal-protocol-dotnet/groups/GroupCipher.cs b/libsignal-protocol-dotnet/groups/GroupCipher.cs
index 4b5d693..4b39221 100644
--- a/libsignal-protocol-dotnet/groups/GroupCipher.cs
+++ b/libsignal-protocol-dotnet/groups/GroupCipher.cs
@@ -19,7 +19,9 @@
 using libsignal.groups.ratchet;
 using libsignal.groups.state;
 using libsignal.protocol;
+using libsignal.state;
 using libsignal.util;
+using System.Threading.Tasks;
 
 namespace libsignal.groups
 {
@@ -127,7 +129,7 @@ public byte[] decrypt(byte[] senderKeyMessageBytes, DecryptionCallback callback)
 
                     byte[] plaintext = getPlainText(senderKey.getIv(), senderKey.getCipherKey(), senderKeyMessage.getCipherText());
 
-                    callback.handlePlaintext(plaintext);
+                    callback.handlePlaintext(plaintext, 931).Wait();//931 random as we don't have the real version
 
                     senderKeyStore.storeSenderKey(senderKeyId, record);
 
@@ -210,7 +212,8 @@ private byte[] getCipherText(byte[] iv, byte[] key, byte[] plaintext)
 
         private class NullDecryptionCallback : DecryptionCallback
         {
-            public void handlePlaintext(byte[] plaintext) { }
-        }
+			public Task handlePlaintext(byte[] plaintext, uint sessionVersion) => Task.CompletedTask;
+
+		}
     }
 }