diff --git a/scheme/lib/sunet-utilities.scm b/scheme/lib/sunet-utilities.scm
index db47d19..81a97bc 100644
--- a/scheme/lib/sunet-utilities.scm
+++ b/scheme/lib/sunet-utilities.scm
@@ -102,7 +102,7 @@
 	  (if (and (integer? field-value) (>= field-value 0)) ;;yes, field value contained only digits
 	      field-value
 	      (http-error (status-code bad-request) req
-			  (format #f "~A header contained characters other than digits" field-name))))
+			  (format #f "~A header contained characters other than digits or whitespace between digits" field-name))))
 	#f)))