diff --git a/packages/kit/src/core/adapter-utils.js b/packages/kit/src/core/adapter-utils.js
index 437219c6ccdc..ca3f61fbab3f 100644
--- a/packages/kit/src/core/adapter-utils.js
+++ b/packages/kit/src/core/adapter-utils.js
@@ -3,12 +3,13 @@
  *
  * This is intended to be used with both requests and responses, to have a consistent body parsing across adapters.
  *
- * @param {string} content_type The `content-type` header of a request/response.
+ * @param {string?} content_type The `content-type` header of a request/response.
  * @returns {boolean}
  */
 export function isContentTypeTextual(content_type) {
+	if (!content_type) return true; // defaults to json
+	const [type] = content_type.split(';'); // get the mime type
 	return (
-		!content_type || // defaults to json
 		content_type === 'text/plain' ||
 		content_type === 'application/json' ||
 		content_type === 'application/x-www-form-urlencoded' ||