diff --git a/pkgs/tools/virtualization/nixos-container/nixos-container.pl b/pkgs/tools/virtualization/nixos-container/nixos-container.pl
index 207177133a57..fefdcd614a56 100755
--- a/pkgs/tools/virtualization/nixos-container/nixos-container.pl
+++ b/pkgs/tools/virtualization/nixos-container/nixos-container.pl
@@ -331,7 +331,7 @@ elsif ($action eq "run") {
 
 elsif ($action eq "show-ip") {
     my $s = read_file($confFile) or die;
-    $s =~ /^LOCAL_ADDRESS=([0-9\.]+)$/m or die "$0: cannot get IP address\n";
+    $s =~ /^LOCAL_ADDRESS=([0-9\.]+)(\/[0-9]+)?$/m or die "$0: cannot get IP address\n";
     print "$1\n";
 }