diff --git a/matrix-sdk-android/src/androidTest/java/org/matrix/android/sdk/common/CryptoTestData.kt b/matrix-sdk-android/src/androidTest/java/org/matrix/android/sdk/common/CryptoTestData.kt
index e01aaef639..693ab28da1 100644
--- a/matrix-sdk-android/src/androidTest/java/org/matrix/android/sdk/common/CryptoTestData.kt
+++ b/matrix-sdk-android/src/androidTest/java/org/matrix/android/sdk/common/CryptoTestData.kt
@@ -19,7 +19,7 @@ package org.matrix.android.sdk.common
 import org.matrix.android.sdk.api.session.Session
 
 data class CryptoTestData(val roomId: String,
-                          val sessions: List<Session> = emptyList()) {
+                          val sessions: MutableList<Session> = mutableListOf()) {
 
     val firstSession: Session
         get() = sessions.first()
diff --git a/matrix-sdk-android/src/androidTest/java/org/matrix/android/sdk/common/CryptoTestHelper.kt b/matrix-sdk-android/src/androidTest/java/org/matrix/android/sdk/common/CryptoTestHelper.kt
index f108cbb105..66fc1348d5 100644
--- a/matrix-sdk-android/src/androidTest/java/org/matrix/android/sdk/common/CryptoTestHelper.kt
+++ b/matrix-sdk-android/src/androidTest/java/org/matrix/android/sdk/common/CryptoTestHelper.kt
@@ -73,7 +73,7 @@ class CryptoTestHelper(private val mTestHelper: CommonTestHelper) {
             }
         }
 
-        return CryptoTestData(roomId, listOf(aliceSession))
+        return CryptoTestData(roomId, mutableListOf(aliceSession))
     }
 
     /**
@@ -139,7 +139,7 @@ class CryptoTestHelper(private val mTestHelper: CommonTestHelper) {
 //        assertNotNull(roomFromBobPOV.powerLevels)
 //        assertTrue(roomFromBobPOV.powerLevels.maySendMessage(bobSession.myUserId))
 
-        return CryptoTestData(aliceRoomId, listOf(aliceSession, bobSession))
+        return CryptoTestData(aliceRoomId, mutableListOf(aliceSession, bobSession))
     }
 
     /**
@@ -157,7 +157,7 @@ class CryptoTestHelper(private val mTestHelper: CommonTestHelper) {
         // wait the initial sync
         SystemClock.sleep(1000)
 
-        return CryptoTestData(aliceRoomId, listOf(aliceSession, cryptoTestData.secondSession!!, samSession))
+        return CryptoTestData(aliceRoomId, mutableListOf(aliceSession, cryptoTestData.secondSession!!, samSession))
     }
 
     /**
@@ -381,4 +381,31 @@ class CryptoTestHelper(private val mTestHelper: CommonTestHelper) {
             }
         }
     }
+
+    fun doE2ETestWithManyMembers(numberOfMembers: Int): CryptoTestData {
+        val aliceSession = mTestHelper.createAccount(TestConstants.USER_ALICE, defaultSessionParams)
+        aliceSession.cryptoService().setWarnOnUnknownDevices(false)
+
+        val roomId = mTestHelper.doSync<String> {
+            aliceSession.createRoom(CreateRoomParams().apply { name = "MyRoom" }, it)
+        }
+        val room = aliceSession.getRoom(roomId)!!
+
+        mTestHelper.runBlockingTest {
+            room.enableEncryption()
+        }
+
+        val cryptoTestData = CryptoTestData(roomId, mutableListOf(aliceSession))
+        for (index in 1 until numberOfMembers) {
+            mTestHelper
+                    .createAccount("User_$index", defaultSessionParams)
+                    .also { session -> mTestHelper.doSync<Unit> { room.invite(session.myUserId, null, it) } }
+                    .also { println("TEST -> " + it.myUserId + " invited") }
+                    .also { session -> mTestHelper.doSync<Unit> { session.joinRoom(room.roomId, null, emptyList(), it) } }
+                    .also { println("TEST -> " + it.myUserId + " joined") }
+                    .also { session -> cryptoTestData.sessions.add(session) }
+        }
+
+        return cryptoTestData
+    }
 }
diff --git a/matrix-sdk-android/src/androidTest/java/org/matrix/android/sdk/session/room/timeline/TimelineWithManyMembersTest.kt b/matrix-sdk-android/src/androidTest/java/org/matrix/android/sdk/session/room/timeline/TimelineWithManyMembersTest.kt
index a0271cb5b9..1a397c1d1c 100644
--- a/matrix-sdk-android/src/androidTest/java/org/matrix/android/sdk/session/room/timeline/TimelineWithManyMembersTest.kt
+++ b/matrix-sdk-android/src/androidTest/java/org/matrix/android/sdk/session/room/timeline/TimelineWithManyMembersTest.kt
@@ -16,6 +16,8 @@
 
 package org.matrix.android.sdk.session.room.timeline
 
+import android.os.SystemClock
+import android.util.Log
 import org.junit.FixMethodOrder
 import org.junit.Test
 import org.junit.runner.RunWith
@@ -29,11 +31,14 @@ import org.matrix.android.sdk.api.session.room.timeline.TimelineSettings
 import org.matrix.android.sdk.common.CommonTestHelper
 import org.matrix.android.sdk.common.CryptoTestHelper
 import java.util.concurrent.CountDownLatch
+import kotlin.test.assertEquals
 
 @RunWith(JUnit4::class)
 @FixMethodOrder(MethodSorters.JVM)
 class TimelineWithManyMembersTest : InstrumentedTest {
 
+    private val NUMBER_OF_MEMBERS = 5
+
     private val commonTestHelper = CommonTestHelper(context())
     private val cryptoTestHelper = CryptoTestHelper(commonTestHelper)
 
@@ -91,4 +96,42 @@ class TimelineWithManyMembersTest : InstrumentedTest {
         }
         samSession.stopSync()
     }
+
+    /**
+     * Ensures when someone sends a message to a crowded room, everyone can decrypt the message.
+     */
+    @Test
+    fun everyone_should_decrypt_message_in_a_crowded_room() {
+        val cryptoTestData = cryptoTestHelper.doE2ETestWithManyMembers(NUMBER_OF_MEMBERS)
+
+        val sessionForFirstMember = cryptoTestData.firstSession
+        val roomForFirstMember = sessionForFirstMember.getRoom(cryptoTestData.roomId)!!
+
+        val firstMessage = "First messages from Alice"
+        commonTestHelper.sendTextMessage(
+                roomForFirstMember,
+                firstMessage,
+                1)
+
+        for (index in 1 until cryptoTestData.sessions.size) {
+            val session = cryptoTestData.sessions[index]
+            val roomForCurrentMember = session.getRoom(cryptoTestData.roomId)!!
+            val timelineForCurrentMember = roomForCurrentMember.createTimeline(null, TimelineSettings(30))
+            timelineForCurrentMember.start()
+
+            session.startSync(true)
+
+            run {
+                val lock = CountDownLatch(1)
+                val eventsListener = commonTestHelper.createEventListener(lock) { snapshot ->
+                    val decryptedMessage = snapshot.firstOrNull()?.root?.getClearContent()?.toModel<MessageContent>()?.body
+                    println("Decrypted Message: $decryptedMessage")
+                    return@createEventListener decryptedMessage?.startsWith(firstMessage).orFalse()
+                }
+                timelineForCurrentMember.addListener(eventsListener)
+                commonTestHelper.await(lock)
+            }
+            session.stopSync()
+        }
+    }
 }