diff --git a/scheme/httpd/cgi-server.scm b/scheme/httpd/cgi-server.scm
index d8e7746..5c6a2b7 100644
--- a/scheme/httpd/cgi-server.scm
+++ b/scheme/httpd/cgi-server.scm
@@ -215,7 +215,7 @@
 
 	  ,@(cond ((get-header headers 'content-length) =>
 		   (lambda (cl)	; Skip initial whitespace (& other non-digits).
-		     (let ((first-digit (string-index cl char-set:numeric))
+		     (let ((first-digit (string-index cl char-set:digit))
 			   (cl-len (string-length cl)))
 		       (if first-digit
 			   `(("CONTENT_LENGTH" . ,(substring cl first-digit cl-len)))