diff --git a/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/session/DefaultSession.kt b/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/session/DefaultSession.kt
index fc76ebd519..32269c9afd 100644
--- a/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/session/DefaultSession.kt
+++ b/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/session/DefaultSession.kt
@@ -131,12 +131,11 @@ internal class DefaultSession @Inject constructor(
         private val toDeviceService: Lazy<ToDeviceService>,
         private val eventStreamService: Lazy<EventStreamService>,
         @UnauthenticatedWithCertificate
-        private val unauthenticatedWithCertificateOkHttpClient: Lazy<OkHttpClient>
+        private val unauthenticatedWithCertificateOkHttpClient: Lazy<OkHttpClient>,
+        private val sessionState: SessionState,
 ) : Session,
         GlobalErrorHandler.Listener {
 
-    private var isOpen = false
-
     private val uiHandler = createUIHandler()
 
     override val isOpenable: Boolean
@@ -144,8 +143,7 @@ internal class DefaultSession @Inject constructor(
 
     @MainThread
     override fun open() {
-        assert(!isOpen)
-        isOpen = true
+        sessionState.setIsOpen(true)
         globalErrorHandler.listener = this
         cryptoService.get().ensureDevice()
         uiHandler.post {
@@ -159,7 +157,7 @@ internal class DefaultSession @Inject constructor(
     }
 
     override fun close() {
-        assert(isOpen)
+        assert(sessionState.isOpen)
         syncService.get().stopSync()
         // timelineEventDecryptor.destroy()
         uiHandler.post {
@@ -170,7 +168,7 @@ internal class DefaultSession @Inject constructor(
         }
         cryptoService.get().close()
         globalErrorHandler.listener = null
-        isOpen = false
+        sessionState.setIsOpen(false)
     }
 
     override suspend fun clearCache() {
diff --git a/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/session/SessionState.kt b/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/session/SessionState.kt
new file mode 100644
index 0000000000..b109a9aa60
--- /dev/null
+++ b/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/session/SessionState.kt
@@ -0,0 +1,33 @@
+/*
+ * Copyright (c) 2022 The Matrix.org Foundation C.I.C.
+ *
+ * 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 org.matrix.android.sdk.internal.session
+
+import javax.inject.Inject
+
+@SessionScope
+internal class SessionState @Inject constructor() {
+    var isOpen = false
+        private set
+
+    /**
+     * Set the new state. Throw if already in the new state.
+     */
+    fun setIsOpen(newState: Boolean) {
+        assert(newState != isOpen)
+        isOpen = newState
+    }
+}
diff --git a/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/session/sync/DefaultSyncService.kt b/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/session/sync/DefaultSyncService.kt
index a97caa10c7..37869b88f9 100644
--- a/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/session/sync/DefaultSyncService.kt
+++ b/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/session/sync/DefaultSyncService.kt
@@ -21,6 +21,7 @@ import org.matrix.android.sdk.api.session.sync.SyncRequestState
 import org.matrix.android.sdk.api.session.sync.SyncService
 import org.matrix.android.sdk.internal.di.SessionId
 import org.matrix.android.sdk.internal.di.WorkManagerProvider
+import org.matrix.android.sdk.internal.session.SessionState
 import org.matrix.android.sdk.internal.session.sync.job.SyncThread
 import org.matrix.android.sdk.internal.session.sync.job.SyncWorker
 import timber.log.Timber
@@ -33,6 +34,7 @@ internal class DefaultSyncService @Inject constructor(
         private val syncThreadProvider: Provider<SyncThread>,
         private val syncTokenStore: SyncTokenStore,
         private val syncRequestStateTracker: SyncRequestStateTracker,
+        private val sessionState: SessionState,
 ) : SyncService {
     private var syncThread: SyncThread? = null
 
@@ -50,8 +52,7 @@ internal class DefaultSyncService @Inject constructor(
 
     override fun startSync(fromForeground: Boolean) {
         Timber.i("Starting sync thread")
-        // TODO How to check that now?
-        // assert(isOpen)
+        assert(sessionState.isOpen)
         val localSyncThread = getSyncThread()
         localSyncThread.setInitialForeground(fromForeground)
         if (!localSyncThread.isAlive) {
@@ -63,8 +64,7 @@ internal class DefaultSyncService @Inject constructor(
     }
 
     override fun stopSync() {
-        // TODO How to check that now?
-        // assert(isOpen)
+        assert(sessionState.isOpen)
         syncThread?.kill()
         syncThread = null
     }