diff --git a/plugins/omemo/src/file_transfer/file_decryptor.vala b/plugins/omemo/src/file_transfer/file_decryptor.vala
index 75adec1a..64a6ef34 100644
--- a/plugins/omemo/src/file_transfer/file_decryptor.vala
+++ b/plugins/omemo/src/file_transfer/file_decryptor.vala
@@ -40,6 +40,7 @@ public class OmemoFileDecryptor : FileDecryptor, Object {
     }
 
     public async InputStream decrypt_file(InputStream encrypted_stream, Conversation conversation, FileTransfer file_transfer, FileReceiveData receive_data) throws FileReceiveError {
+        const uint KEY_SIZE = 32;
         try {
             OmemoHttpFileReceiveData? omemo_http_receive_data = receive_data as OmemoHttpFileReceiveData;
             if (omemo_http_receive_data == null) assert(false);
@@ -48,8 +49,8 @@ public class OmemoFileDecryptor : FileDecryptor, Object {
             MatchInfo match_info;
             this.url_regex.match(omemo_http_receive_data.original_url, 0, out match_info);
             uint8[] iv_and_key = hex_to_bin(match_info.fetch(2).up());
-            uint8[] iv = iv_and_key[0:iv_and_key.length-16];
-            uint8[] key = iv_and_key[iv_and_key.length-16:iv_and_key.length];
+            uint8[] iv = iv_and_key[0:iv_and_key.length-KEY_SIZE];
+            uint8[] key = iv_and_key[iv_and_key.length-KEY_SIZE:iv_and_key.length];
 
             file_transfer.encryption = Encryption.OMEMO;
             debug("Decrypting file %s from %s", file_transfer.file_name, file_transfer.server_file_name);