skoczian, please test with this patch :
diff --git a/firebirdsql/fbcore.py b/firebirdsql/fbcore.py index 3d301fc..128295f 100755 --- a/firebirdsql/fbcore.py +++ b/firebirdsql/fbcore.py @@ -406,9 +406,8 @@ class cursor: for param in params: # Convert str/bytes parameter to blob id if type(param) == str: param = self.connection.str_to_bytes(param) - else: - cooked_params.append(param) - continue + cooked_params.append(param) + continue self.connection._op_create_blob2() (blob_handle, blob_id, buf2) = self.connection._op_response() seg_size = self.connection.buffer_length