diff --git a/capella2polarion/data_model/work_item_attachments.py b/capella2polarion/data_model/work_item_attachments.py
index d35ef25..62f2add 100644
--- a/capella2polarion/data_model/work_item_attachments.py
+++ b/capella2polarion/data_model/work_item_attachments.py
@@ -115,8 +115,12 @@ def content_checksum(self) -> str:
         if self._checksum is None:
             try:
                 elk_input = self.diagram.elk_input_data(self.render_params)
+                if isinstance(elk_input, tuple):
+                    input_str = ";".join(eit.json() for eit in elk_input)
+                else:
+                    input_str = elk_input.json()
                 self._checksum = hashlib.sha256(
-                    elk_input.json().encode("utf-8")
+                    input_str.encode("utf-8")
                 ).hexdigest()
             except Exception as e:
                 logger.error(