diff --git a/.idea/dictionaries/bmarty.xml b/.idea/dictionaries/bmarty.xml
index 7e9a9e1b03..1f93d1feee 100644
--- a/.idea/dictionaries/bmarty.xml
+++ b/.idea/dictionaries/bmarty.xml
@@ -25,6 +25,7 @@
       <w>signup</w>
       <w>ssss</w>
       <w>threepid</w>
+      <w>unwedging</w>
     </words>
   </dictionary>
 </component>
\ No newline at end of file
diff --git a/matrix-sdk-android/src/androidTest/java/im/vector/matrix/android/common/CryptoTestHelper.kt b/matrix-sdk-android/src/androidTest/java/im/vector/matrix/android/common/CryptoTestHelper.kt
index 826c70a63f..1084dc423d 100644
--- a/matrix-sdk-android/src/androidTest/java/im/vector/matrix/android/common/CryptoTestHelper.kt
+++ b/matrix-sdk-android/src/androidTest/java/im/vector/matrix/android/common/CryptoTestHelper.kt
@@ -22,6 +22,7 @@ import im.vector.matrix.android.api.session.Session
 import im.vector.matrix.android.api.session.events.model.Event
 import im.vector.matrix.android.api.session.events.model.EventType
 import im.vector.matrix.android.api.session.events.model.toContent
+import im.vector.matrix.android.api.session.room.Room
 import im.vector.matrix.android.api.session.room.model.Membership
 import im.vector.matrix.android.api.session.room.model.RoomSummary
 import im.vector.matrix.android.api.session.room.model.create.CreateRoomParams
@@ -40,7 +41,6 @@ import kotlinx.coroutines.runBlocking
 import org.junit.Assert.assertEquals
 import org.junit.Assert.assertNotNull
 import org.junit.Assert.assertNull
-import org.junit.Assert.assertTrue
 import java.util.HashMap
 import java.util.concurrent.CountDownLatch
 
@@ -140,64 +140,38 @@ class CryptoTestHelper(private val mTestHelper: CommonTestHelper) {
      * @return Alice, Bob and Sam session
      */
     fun doE2ETestWithAliceAndBobAndSamInARoom(): CryptoTestData {
-        val statuses = HashMap<String, String>()
-
         val cryptoTestData = doE2ETestWithAliceAndBobInARoom()
         val aliceSession = cryptoTestData.firstSession
         val aliceRoomId = cryptoTestData.roomId
 
         val room = aliceSession.getRoom(aliceRoomId)!!
 
-        val samSession = mTestHelper.createAccount(TestConstants.USER_SAM, defaultSessionParams)
-
-        val lock1 = CountDownLatch(2)
-
-//        val samEventListener = object : MXEventListener() {
-//            override fun onNewRoom(roomId: String) {
-//                if (TextUtils.equals(roomId, aliceRoomId)) {
-//                    if (!statuses.containsKey("onNewRoom")) {
-//                        statuses["onNewRoom"] = "onNewRoom"
-//                        lock1.countDown()
-//                    }
-//                }
-//            }
-//        }
-//
-//        samSession.dataHandler.addListener(samEventListener)
-
-        room.invite(samSession.myUserId, null, object : TestMatrixCallback<Unit>(lock1) {
-            override fun onSuccess(data: Unit) {
-                statuses["invite"] = "invite"
-                super.onSuccess(data)
-            }
-        })
-
-        mTestHelper.await(lock1)
-
-        assertTrue(statuses.containsKey("invite") && statuses.containsKey("onNewRoom"))
-
-//        samSession.dataHandler.removeListener(samEventListener)
-
-        val lock2 = CountDownLatch(1)
-
-        samSession.joinRoom(aliceRoomId, null, object : TestMatrixCallback<Unit>(lock2) {
-            override fun onSuccess(data: Unit) {
-                statuses["joinRoom"] = "joinRoom"
-                super.onSuccess(data)
-            }
-        })
-
-        mTestHelper.await(lock2)
-        assertTrue(statuses.containsKey("joinRoom"))
+        val samSession = createSamAccountAndInviteToTheRoom(room)
 
         // wait the initial sync
         SystemClock.sleep(1000)
 
-//        samSession.dataHandler.removeListener(samEventListener)
-
         return CryptoTestData(aliceSession, aliceRoomId, cryptoTestData.secondSession, samSession)
     }
 
+    /**
+     * Create Sam account and invite him in the room. He will accept the invitation
+     * @Return Sam session
+     */
+    fun createSamAccountAndInviteToTheRoom(room: Room): Session {
+        val samSession = mTestHelper.createAccount(TestConstants.USER_SAM, defaultSessionParams)
+
+        mTestHelper.doSync<Unit> {
+            room.invite(samSession.myUserId, null, it)
+        }
+
+        mTestHelper.doSync<Unit> {
+            samSession.joinRoom(room.roomId, null, it)
+        }
+
+        return samSession
+    }
+
     /**
      * @return Alice and Bob sessions
      */
diff --git a/matrix-sdk-android/src/androidTest/java/im/vector/matrix/android/internal/crypto/UnwedgingTest.kt b/matrix-sdk-android/src/androidTest/java/im/vector/matrix/android/internal/crypto/UnwedgingTest.kt
new file mode 100644
index 0000000000..ce5873b451
--- /dev/null
+++ b/matrix-sdk-android/src/androidTest/java/im/vector/matrix/android/internal/crypto/UnwedgingTest.kt
@@ -0,0 +1,174 @@
+/*
+ * Copyright (c) 2020 New Vector Ltd
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package im.vector.matrix.android.internal.crypto
+
+import androidx.test.ext.junit.runners.AndroidJUnit4
+import im.vector.matrix.android.InstrumentedTest
+import im.vector.matrix.android.api.session.events.model.EventType
+import im.vector.matrix.android.api.session.room.timeline.Timeline
+import im.vector.matrix.android.api.session.room.timeline.TimelineEvent
+import im.vector.matrix.android.api.session.room.timeline.TimelineSettings
+import im.vector.matrix.android.common.CommonTestHelper
+import im.vector.matrix.android.common.CryptoTestHelper
+import org.amshove.kluent.shouldBe
+import org.amshove.kluent.shouldBeEqualTo
+import org.junit.Before
+import org.junit.FixMethodOrder
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.junit.runners.MethodSorters
+import java.util.concurrent.CountDownLatch
+
+/**
+ * Ref:
+ * - https://github.com/matrix-org/matrix-doc/pull/1719
+ * - https://matrix.org/docs/spec/client_server/latest#recovering-from-undecryptable-messages
+ * - https://github.com/matrix-org/matrix-js-sdk/pull/780
+ * - https://github.com/matrix-org/matrix-ios-sdk/pull/778
+ * - https://github.com/matrix-org/matrix-ios-sdk/pull/784
+ */
+@RunWith(AndroidJUnit4::class)
+@FixMethodOrder(MethodSorters.JVM)
+class UnwedgingTest : InstrumentedTest {
+
+    private lateinit var messagesReceivedByBob: List<TimelineEvent>
+    private val mTestHelper = CommonTestHelper(context())
+    private val mCryptoTestHelper = CryptoTestHelper(mTestHelper)
+
+    @Before
+    fun init() {
+        messagesReceivedByBob = emptyList()
+    }
+
+    /**
+     * - Alice & Bob in a e2e room
+     * - Alice sends a 1st message with a 1st megolm session
+     * - Store the olm session between A&B devices
+     * - Alice sends a 2nd message with a 2nd megolm session
+     * - Simulate Alice using a backup of her OS and make her crypto state like after the first message
+     * - Alice sends a 3rd message with a 3rd megolm session but a wedged olm session
+     *
+     * What Bob must see:
+     * -> No issue with the 2 first messages
+     * -> The third event must fail to decrypt at first because Bob the olm session is wedged
+     * -> This is automatically fixed after SDKs restarted the olm session
+     */
+    @Test
+    fun testUnwedging() {
+        val cryptoTestData = mCryptoTestHelper.doE2ETestWithAliceAndBobInARoom()
+
+        val aliceSession = cryptoTestData.firstSession
+        val aliceRoomId = cryptoTestData.roomId
+        val bobSession = cryptoTestData.secondSession!!
+
+        val aliceCryptoStore = (aliceSession.cryptoService() as DefaultCryptoService).cryptoStoreForTesting
+
+        bobSession.cryptoService().setWarnOnUnknownDevices(false)
+
+        aliceSession.cryptoService().setWarnOnUnknownDevices(false)
+
+        val roomFromBobPOV = bobSession.getRoom(aliceRoomId)!!
+        val roomFromAlicePOV = aliceSession.getRoom(aliceRoomId)!!
+
+        val bobTimeline = roomFromBobPOV.createTimeline(null, TimelineSettings(20))
+        bobTimeline.start()
+
+        var latch = CountDownLatch(1)
+        var bobEventsListener = createEventListener(latch, 1)
+        bobTimeline.addListener(bobEventsListener)
+        messagesReceivedByBob = emptyList()
+
+        // - Alice sends a 1st message with a 1st megolm session
+        roomFromAlicePOV.sendTextMessage("First message")
+
+        // Wait for the message to be received by Bob
+        mTestHelper.await(latch)
+        bobTimeline.removeListener(bobEventsListener)
+
+        messagesReceivedByBob.size shouldBe 1
+
+        //  - Store the olm session between A&B devices
+        // Let us pickle our session with bob here so we can later unpickle it
+        // and wedge our session.
+        val sessionIdsForBob = aliceCryptoStore.getDeviceSessionIds(bobSession.cryptoService().getMyDevice().identityKey()!!)
+        sessionIdsForBob!!.size shouldBe 1
+        val olmSession = aliceCryptoStore.getDeviceSession(sessionIdsForBob.first(), bobSession.cryptoService().getMyDevice().identityKey()!!)!!
+
+        // Sam join the room
+        val samSession = mCryptoTestHelper.createSamAccountAndInviteToTheRoom(roomFromAlicePOV)
+
+        latch = CountDownLatch(1)
+        bobEventsListener = createEventListener(latch, 2)
+        bobTimeline.addListener(bobEventsListener)
+        messagesReceivedByBob = emptyList()
+
+        // - Alice sends a 2nd message with a 2nd megolm session
+        roomFromAlicePOV.sendTextMessage("Second message")
+
+        // Wait for the message to be received by Bob
+        mTestHelper.await(latch)
+        bobTimeline.removeListener(bobEventsListener)
+
+        messagesReceivedByBob.size shouldBe 2
+
+        // Let us wedge the session now. Set crypto state like after the first message
+        aliceCryptoStore.storeSession(olmSession, bobSession.cryptoService().getMyDevice().identityKey()!!)
+
+        latch = CountDownLatch(1)
+        bobEventsListener = createEventListener(latch, 3)
+        bobTimeline.addListener(bobEventsListener)
+        messagesReceivedByBob = emptyList()
+
+        // - Alice sends a 3rd message with a 3rd megolm session but a wedged olm session
+        roomFromAlicePOV.sendTextMessage("Third message")
+
+        // Wait for the message to be received by Bob
+        mTestHelper.await(latch)
+        bobTimeline.removeListener(bobEventsListener)
+
+        messagesReceivedByBob.size shouldBe 3
+
+        messagesReceivedByBob[0].root.getClearType() shouldBeEqualTo EventType.ENCRYPTED
+        messagesReceivedByBob[1].root.getClearType() shouldBeEqualTo EventType.MESSAGE
+        messagesReceivedByBob[2].root.getClearType() shouldBeEqualTo EventType.MESSAGE
+
+        bobTimeline.dispose()
+
+        cryptoTestData.cleanUp(mTestHelper)
+        mTestHelper.signOutAndClose(samSession)
+    }
+
+    private fun createEventListener(latch: CountDownLatch, expectedNumberOfMessages: Int): Timeline.Listener {
+        return object : Timeline.Listener {
+            override fun onTimelineFailure(throwable: Throwable) {
+                // noop
+            }
+
+            override fun onNewTimelineEvents(eventIds: List<String>) {
+                // noop
+            }
+
+            override fun onTimelineUpdated(snapshot: List<TimelineEvent>) {
+                messagesReceivedByBob = snapshot.filter { it.root.type == EventType.ENCRYPTED }
+
+                if (messagesReceivedByBob.size == expectedNumberOfMessages) {
+                    latch.countDown()
+                }
+            }
+        }
+    }
+}
diff --git a/matrix-sdk-android/src/main/java/im/vector/matrix/android/internal/crypto/DefaultCryptoService.kt b/matrix-sdk-android/src/main/java/im/vector/matrix/android/internal/crypto/DefaultCryptoService.kt
index aceead8ea0..61a072ece6 100755
--- a/matrix-sdk-android/src/main/java/im/vector/matrix/android/internal/crypto/DefaultCryptoService.kt
+++ b/matrix-sdk-android/src/main/java/im/vector/matrix/android/internal/crypto/DefaultCryptoService.kt
@@ -21,6 +21,7 @@ package im.vector.matrix.android.internal.crypto
 import android.content.Context
 import android.os.Handler
 import android.os.Looper
+import androidx.annotation.VisibleForTesting
 import androidx.lifecycle.LiveData
 import com.squareup.moshi.Types
 import com.zhuinden.monarchy.Monarchy
@@ -1192,4 +1193,11 @@ internal class DefaultCryptoService @Inject constructor(
     override fun getGossipingEventsTrail(): List<Event> {
         return cryptoStore.getGossipingEventsTrail()
     }
+
+    /* ==========================================================================================
+     * For test only
+     * ========================================================================================== */
+
+    @VisibleForTesting
+    val cryptoStoreForTesting = cryptoStore
 }