diff --git a/fetch.js b/fetch.js
index 12c45f29562d91596479e5be59e0284345ffba20..8bfb041edfb8d8d3caff2c98ccbd8ff4f9d02f48 100644
--- a/fetch.js
+++ b/fetch.js
@@ -50,7 +50,7 @@ function normalizeName(name) {
     name = String(name)
   }
   if (/[^a-z0-9\-#$%&'*+.^_`|~!]/i.test(name) || name === '') {
-    throw new TypeError('Invalid character in header field name')
+    throw new TypeError('Invalid character in header field name: ' + name)
   }
   return name.toLowerCase()
 }