diff --git a/extract-fields.ini b/extract-fields.ini
index f97d5ee..f9f5087 100644
--- a/extract-fields.ini
+++ b/extract-fields.ini
@@ -25,7 +25,7 @@
 value = get('static_data.summary.titles.title').filter(title => title.type === "item").map(title => title.content).join('|')
 
 path = abstract
-value = get('static_data.fullrecord_metadata.abstracts.abstract.abstract_text.p', []).castArray().map(s => s.replace(/<[^>]*>/g, "").replace("Key Points", "")).join(" ; ")
+value = get('static_data.fullrecord_metadata.abstracts.abstract.abstract_text.p', []).castArray().map(s => String(s).replace(/<[^>]*>/g, "").replace("Key Points", "")).join(" ; ")
 
 path = publication_year
 value = get('static_data.summary.pub_info.pubyear')