diff --git a/AnkiDroid/src/main/java/com/ichi2/anki/DeckPicker.kt b/AnkiDroid/src/main/java/com/ichi2/anki/DeckPicker.kt
index 441e563588fe..92a2bae79dd7 100644
--- a/AnkiDroid/src/main/java/com/ichi2/anki/DeckPicker.kt
+++ b/AnkiDroid/src/main/java/com/ichi2/anki/DeckPicker.kt
@@ -619,7 +619,7 @@ open class DeckPicker :
                 return true
             }
         })
-        if (colIsOpen()) {
+        if (colIsOpen() && !CollectionHelper.getInstance().isCollectionLocked) {
             displaySyncBadge(menu)
 
             // Show / hide undo
diff --git a/AnkiDroid/src/main/java/com/ichi2/anki/Sync.kt b/AnkiDroid/src/main/java/com/ichi2/anki/Sync.kt
index 6254682b95d4..ea74974e3ca3 100644
--- a/AnkiDroid/src/main/java/com/ichi2/anki/Sync.kt
+++ b/AnkiDroid/src/main/java/com/ichi2/anki/Sync.kt
@@ -166,16 +166,19 @@ private suspend fun handleDownload(
         extractProgress = fullDownloadProgress(col.tr.syncDownloadingFromAnkiweb()),
         onCancel = ::cancelSync
     ) {
-        col.createBackup(
-            BackupManager.getBackupDirectoryFromCollection(col.path),
-            force = true,
-            waitForCompletion = true
-        )
-        col.close(save = true, downgrade = false, forFullSync = true)
+        val helper = CollectionHelper.getInstance()
+        helper.lockCollection()
         try {
+            col.createBackup(
+                BackupManager.getBackupDirectoryFromCollection(col.path),
+                force = true,
+                waitForCompletion = true
+            )
+            col.close(save = true, downgrade = false, forFullSync = true)
             col.fullDownload(auth)
         } finally {
             col.reopen(afterFullSync = true)
+            helper.unlockCollection()
         }
     }
 
@@ -193,11 +196,14 @@ private suspend fun handleUpload(
         extractProgress = fullDownloadProgress(col.tr.syncUploadingToAnkiweb()),
         onCancel = ::cancelSync
     ) {
+        val helper = CollectionHelper.getInstance()
+        helper.lockCollection()
         col.close(save = true, downgrade = false, forFullSync = true)
         try {
             col.fullUpload(auth)
         } finally {
             col.reopen(afterFullSync = true)
+            helper.unlockCollection()
         }
     }
     Timber.i("Full Upload Completed")
diff --git a/AnkiDroid/src/main/java/com/ichi2/utils/SyncStatus.kt b/AnkiDroid/src/main/java/com/ichi2/utils/SyncStatus.kt
index 3f6d0420acfe..eac41f2acbf0 100644
--- a/AnkiDroid/src/main/java/com/ichi2/utils/SyncStatus.kt
+++ b/AnkiDroid/src/main/java/com/ichi2/utils/SyncStatus.kt
@@ -30,14 +30,15 @@ enum class SyncStatus {
 
         @JvmStatic
         fun getSyncStatus(getCol: Supplier<Collection>): SyncStatus {
-            val col: Collection
-            col = try {
-                getCol.get()
+            return try {
+                val col = getCol.get()
+                // may fail when the collection is closed for a full sync,
+                // as col.db is null
+                getSyncStatus(col)
             } catch (e: Exception) {
                 Timber.w(e)
                 return INCONCLUSIVE
             }
-            return getSyncStatus(col)
         }
 
         @JvmStatic