diff --git a/collects/net/dns-unit.ss b/collects/net/dns-unit.ss
index 897bba3730..4f15164e90 100644
--- a/collects/net/dns-unit.ss
+++ b/collects/net/dns-unit.ss
@@ -336,7 +336,7 @@
 	       (let ([l (read-line)])
 		 (or (and (string? l)
 			  (let ([m (regexp-match
-				    (format "nameserver[ ~a]+([0-9]+[.][0-9]+[.][0-9]+[.][0-9]+)" #\tab)
+				    #rx"nameserver[ \t]+([0-9]+[.][0-9]+[.][0-9]+[.][0-9]+)"
 				    l)])
 			    (and m (cadr m))))
 		     (and (not (eof-object? l))