-        if (mUriMatcher.match(uri) != SINGLE_FILE &&
-                mUriMatcher.match(uri) != ROOT_DIRECTORY) {
-            //Log_OC.e(TAG, "Inserting invalid URI: " + uri);
-            throw new IllegalArgumentException("Unknown uri id: " + uri);
-        }
+        switch (mUriMatcher.match(uri)){
+        case ROOT_DIRECTORY:
+        case SINGLE_FILE:
+            String remotePath = values.getAsString(ProviderTableMeta.FILE_PATH);
+            String accountName = values.getAsString(ProviderTableMeta.FILE_ACCOUNT_OWNER);
+            String[] projection = new String[] {ProviderTableMeta._ID, ProviderTableMeta.FILE_PATH, ProviderTableMeta.FILE_ACCOUNT_OWNER };
+            String where = ProviderTableMeta.FILE_PATH + "=? AND " + ProviderTableMeta.FILE_ACCOUNT_OWNER + "=?";
+            String[] whereArgs = new String[] {remotePath, accountName};
+            Cursor doubleCheck = query(db, uri, projection, where, whereArgs, null);
+            if (doubleCheck == null || !doubleCheck.moveToFirst()) {    // ugly patch; serious refactorization is needed to reduce work in FileDataStorageManager and bring it to FileContentProvider 
+                long rowId = db.insert(ProviderTableMeta.FILE_TABLE_NAME, null, values);
+                if (rowId > 0) {
+                    Uri insertedFileUri = ContentUris.withAppendedId(ProviderTableMeta.CONTENT_URI_FILE, rowId);
+                    //Log_OC.d(TAG, "Inserted " + values.getAsString(ProviderTableMeta.FILE_PATH) + " at provider " + this);
+                    return insertedFileUri;
+                } else {
+                    //Log_OC.d(TAG, "Error while inserting " + values.getAsString(ProviderTableMeta.FILE_PATH)  + " at provider " + this);
+                    throw new SQLException("ERROR " + uri);
+                }
+            } else {
+                // file is already inserted; race condition, let's avoid a duplicated entry
+                Uri insertedFileUri = ContentUris.withAppendedId(ProviderTableMeta.CONTENT_URI_FILE, doubleCheck.getLong(doubleCheck.getColumnIndex(ProviderTableMeta._ID)));
+                doubleCheck.close();