jimlib/net-utils.tcl | 2 +-

diff --git a/jimlib/net-utils.tcl b/jimlib/net-utils.tcl
index cb217988cd92c2790de17b9601525c529633ab2cc88124c8036586481c1540b3..9a8bbd6f5377ad69c6deede5f566fc11152181d51ab72476feba8279f5fc4580 100644
--- a/jimlib/net-utils.tcl
+++ b/jimlib/net-utils.tcl
@@ -53,7 +53,7 @@         set addr [ipv4::contract $addr]
     } else {
         package require ipv6
         if {[ipv6::isIpv6 $addr] != 1} {error "invalid IPv6 format"}
-        set addr [ipv6::contract $addr]
+        set addr [string tolower [ipv6::contract $addr]]
     }
     package require check-utils
     set prefixlen [parse-int $prefixlen $maxlen]