diff --git a/CHANGELOG.md b/CHANGELOG.md
index dd6f9d4aac..e75747bdec 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,6 +12,7 @@
 * Cache notification callback JNI references at startup to ensure that symbols can be resolved in core callbacks. (Issue [#1577](https://github.com/realm/realm-kotlin/issues/1577))
 * Using `Realm.asFlow()` could miss an update if a write was started right after opening the Realm. (Issue [#1582](https://github.com/realm/realm-kotlin/issues/1582)) 
 * Snapshot publishing with Github Action. (Issue [#1654](https://github.com/realm/realm-kotlin/issues/1654) [JIRA](https://jira.mongodb.org/browse/RKOTLIN-1018))
+* [Sync] `NullPointerException` while waiting for the synchronization of a subscription set if the client was set in `AwaitingMark` state. (Issue [#1671](https://github.com/realm/realm-kotlin/issues/1671) [JIRA](https://jira.mongodb.org/browse/RKOTLIN-1027))
 
 ### Compatibility
 * File format: Generates Realms with file format v23.
diff --git a/packages/cinterop/src/androidInstrumentedTest/kotlin/io/realm/kotlin/test/sync/SyncEnumTests.kt b/packages/cinterop/src/androidInstrumentedTest/kotlin/io/realm/kotlin/test/sync/SyncEnumTests.kt
index 4d12f28409..aba2ef41a4 100644
--- a/packages/cinterop/src/androidInstrumentedTest/kotlin/io/realm/kotlin/test/sync/SyncEnumTests.kt
+++ b/packages/cinterop/src/androidInstrumentedTest/kotlin/io/realm/kotlin/test/sync/SyncEnumTests.kt
@@ -22,6 +22,7 @@ import io.realm.kotlin.internal.interop.ErrorCode
 import io.realm.kotlin.internal.interop.realm_auth_provider_e
 import io.realm.kotlin.internal.interop.realm_errno_e
 import io.realm.kotlin.internal.interop.realm_error_category_e
+import io.realm.kotlin.internal.interop.realm_flx_sync_subscription_set_state_e
 import io.realm.kotlin.internal.interop.realm_sync_client_metadata_mode_e
 import io.realm.kotlin.internal.interop.realm_sync_connection_state_e
 import io.realm.kotlin.internal.interop.realm_sync_errno_connection_e
@@ -33,6 +34,7 @@ import io.realm.kotlin.internal.interop.realm_user_state_e
 import io.realm.kotlin.internal.interop.realm_web_socket_errno_e
 import io.realm.kotlin.internal.interop.sync.AuthProvider
 import io.realm.kotlin.internal.interop.sync.CoreConnectionState
+import io.realm.kotlin.internal.interop.sync.CoreSubscriptionSetState
 import io.realm.kotlin.internal.interop.sync.CoreSyncSessionState
 import io.realm.kotlin.internal.interop.sync.CoreUserState
 import io.realm.kotlin.internal.interop.sync.MetadataMode
@@ -137,6 +139,13 @@ class SyncEnumTests {
         }
     }
 
+    @Test
+    fun syncSubscriptionSetState() {
+        checkEnum(realm_flx_sync_subscription_set_state_e::class) { nativeValue ->
+            CoreSubscriptionSetState.of(nativeValue)
+        }
+    }
+
     @Test
     fun websocketResultCode() {
         checkEnum(realm_sync_socket_callback_result_e::class) { nativeValue ->
diff --git a/packages/cinterop/src/commonMain/kotlin/io/realm/kotlin/internal/interop/sync/CoreSubscriptionSetState.kt b/packages/cinterop/src/commonMain/kotlin/io/realm/kotlin/internal/interop/sync/CoreSubscriptionSetState.kt
index 2425def8f5..6544f6653e 100644
--- a/packages/cinterop/src/commonMain/kotlin/io/realm/kotlin/internal/interop/sync/CoreSubscriptionSetState.kt
+++ b/packages/cinterop/src/commonMain/kotlin/io/realm/kotlin/internal/interop/sync/CoreSubscriptionSetState.kt
@@ -26,5 +26,6 @@ expect enum class CoreSubscriptionSetState {
     RLM_SYNC_SUBSCRIPTION_BOOTSTRAPPING,
     RLM_SYNC_SUBSCRIPTION_COMPLETE,
     RLM_SYNC_SUBSCRIPTION_ERROR,
-    RLM_SYNC_SUBSCRIPTION_SUPERSEDED;
+    RLM_SYNC_SUBSCRIPTION_SUPERSEDED,
+    RLM_SYNC_SUBSCRIPTION_AWAITING_MARK;
 }
diff --git a/packages/cinterop/src/jvm/kotlin/io/realm/kotlin/internal/interop/sync/CoreSubscriptionSetState.kt b/packages/cinterop/src/jvm/kotlin/io/realm/kotlin/internal/interop/sync/CoreSubscriptionSetState.kt
index e134e03cca..dbcfe0f8ca 100644
--- a/packages/cinterop/src/jvm/kotlin/io/realm/kotlin/internal/interop/sync/CoreSubscriptionSetState.kt
+++ b/packages/cinterop/src/jvm/kotlin/io/realm/kotlin/internal/interop/sync/CoreSubscriptionSetState.kt
@@ -25,11 +25,12 @@ actual enum class CoreSubscriptionSetState(override val nativeValue: Int) : Nati
     RLM_SYNC_SUBSCRIPTION_BOOTSTRAPPING(realm_flx_sync_subscription_set_state_e.RLM_SYNC_SUBSCRIPTION_BOOTSTRAPPING),
     RLM_SYNC_SUBSCRIPTION_COMPLETE(realm_flx_sync_subscription_set_state_e.RLM_SYNC_SUBSCRIPTION_COMPLETE),
     RLM_SYNC_SUBSCRIPTION_ERROR(realm_flx_sync_subscription_set_state_e.RLM_SYNC_SUBSCRIPTION_ERROR),
-    RLM_SYNC_SUBSCRIPTION_SUPERSEDED(realm_flx_sync_subscription_set_state_e.RLM_SYNC_SUBSCRIPTION_SUPERSEDED);
+    RLM_SYNC_SUBSCRIPTION_SUPERSEDED(realm_flx_sync_subscription_set_state_e.RLM_SYNC_SUBSCRIPTION_SUPERSEDED),
+    RLM_SYNC_SUBSCRIPTION_AWAITING_MARK(realm_flx_sync_subscription_set_state_e.RLM_SYNC_SUBSCRIPTION_AWAITING_MARK);
 
     companion object {
         fun of(state: Int): CoreSubscriptionSetState {
-            for (value in values()) {
+            for (value in entries) {
                 if (value.nativeValue == state) {
                     return value
                 }
diff --git a/packages/cinterop/src/nativeDarwin/kotlin/io/realm/kotlin/internal/interop/sync/CoreSubscriptionSetState.kt b/packages/cinterop/src/nativeDarwin/kotlin/io/realm/kotlin/internal/interop/sync/CoreSubscriptionSetState.kt
index 554d0f62ee..02bbaf2cfc 100644
--- a/packages/cinterop/src/nativeDarwin/kotlin/io/realm/kotlin/internal/interop/sync/CoreSubscriptionSetState.kt
+++ b/packages/cinterop/src/nativeDarwin/kotlin/io/realm/kotlin/internal/interop/sync/CoreSubscriptionSetState.kt
@@ -26,11 +26,12 @@ actual enum class CoreSubscriptionSetState(
     RLM_SYNC_SUBSCRIPTION_BOOTSTRAPPING(realm_wrapper.RLM_SYNC_SUBSCRIPTION_BOOTSTRAPPING),
     RLM_SYNC_SUBSCRIPTION_COMPLETE(realm_wrapper.RLM_SYNC_SUBSCRIPTION_COMPLETE),
     RLM_SYNC_SUBSCRIPTION_ERROR(realm_wrapper.RLM_SYNC_SUBSCRIPTION_ERROR),
-    RLM_SYNC_SUBSCRIPTION_SUPERSEDED(realm_wrapper.RLM_SYNC_SUBSCRIPTION_SUPERSEDED);
+    RLM_SYNC_SUBSCRIPTION_SUPERSEDED(realm_wrapper.RLM_SYNC_SUBSCRIPTION_SUPERSEDED),
+    RLM_SYNC_SUBSCRIPTION_AWAITING_MARK(realm_wrapper.RLM_SYNC_SUBSCRIPTION_AWAITING_MARK);
 
     companion object {
         fun of(state: realm_flx_sync_subscription_set_state_e): CoreSubscriptionSetState {
-            for (value in values()) {
+            for (value in entries) {
                 if (value.nativeValue == state) {
                     return value
                 }
diff --git a/packages/library-sync/src/commonMain/kotlin/io/realm/kotlin/mongodb/internal/BaseSubscriptionSetImpl.kt b/packages/library-sync/src/commonMain/kotlin/io/realm/kotlin/mongodb/internal/BaseSubscriptionSetImpl.kt
index 2ecf15e5d9..aa73fe4586 100644
--- a/packages/library-sync/src/commonMain/kotlin/io/realm/kotlin/mongodb/internal/BaseSubscriptionSetImpl.kt
+++ b/packages/library-sync/src/commonMain/kotlin/io/realm/kotlin/mongodb/internal/BaseSubscriptionSetImpl.kt
@@ -129,6 +129,8 @@ internal abstract class BaseSubscriptionSetImpl<T : BaseRealm>(
                     SubscriptionSetState.ERROR
                 CoreSubscriptionSetState.RLM_SYNC_SUBSCRIPTION_SUPERSEDED ->
                     SubscriptionSetState.SUPERCEDED
+                CoreSubscriptionSetState.RLM_SYNC_SUBSCRIPTION_AWAITING_MARK ->
+                    SubscriptionSetState.AWAITING_MARK
                 else -> TODO("Unsupported state: $coreState")
             }
         }
diff --git a/packages/library-sync/src/commonMain/kotlin/io/realm/kotlin/mongodb/sync/SubscriptionSetState.kt b/packages/library-sync/src/commonMain/kotlin/io/realm/kotlin/mongodb/sync/SubscriptionSetState.kt
index b30ee965ac..dc9b98c56c 100644
--- a/packages/library-sync/src/commonMain/kotlin/io/realm/kotlin/mongodb/sync/SubscriptionSetState.kt
+++ b/packages/library-sync/src/commonMain/kotlin/io/realm/kotlin/mongodb/sync/SubscriptionSetState.kt
@@ -55,5 +55,11 @@ public enum class SubscriptionSetState {
      * are ignored by the server. Get the latest subscription set by calling
      * [SubscriptionSet.refresh].
      */
-    SUPERCEDED;
+    SUPERCEDED,
+
+    /**
+     * The last bootstrap message containing the initial state for this subscription set has been received. The
+     * client is awaiting a mark message to mark this subscription as fully caught up to history.
+     */
+    AWAITING_MARK;
 }