diff --git a/src/parser.js b/src/parser.js
index a166e70..9a2b5bb 100644
--- a/src/parser.js
+++ b/src/parser.js
@@ -226,6 +226,10 @@ function populateFrontmatter(posts) {
 		// inject custom taxonomy slugs into frontmatter, each taxonomy as its own field
 		Object.entries(post.customTaxonomies).forEach(([domain, slugs]) => {
 			if (slugs.length > 0) {
+				if (post.frontmatter.hasOwnProperty(domain)) {
+					console.warn(`⚠️  Skipping custom taxonomy '${domain}' on post '${post.slug}' because it conflicts with an existing frontmatter field.`);
+					return;
+				}
 				post.frontmatter[domain] = slugs;
 			}
 		});