diff --git a/tei2imxml.py b/tei2imxml.py
index 4297040..c76ed1f 100755
--- a/tei2imxml.py
+++ b/tei2imxml.py
@@ -618,7 +618,11 @@ def handle_refs_hyperimage(ref):
 
         fn_parent = footnote.getparent()
         # we assert here that the parent of a footnote is always a paragraph or a quote
-        footnote_id = footnote.xpath("@xml:id")[0]
+        try:
+            footnote_id = footnote.xpath("@xml:id")[0]
+        except IndexError:
+            logging.error("Found footnote without xml:id. Exiting.")
+            sys.exit(1)
 
         # logging.debug(f"The prefix of fn_parent is {fn_parent.prefix}.")