diff --git a/nixos/modules/config/update-users-groups.pl b/nixos/modules/config/update-users-groups.pl
index 5a21cb45d52..4368ec24ea9 100644
--- a/nixos/modules/config/update-users-groups.pl
+++ b/nixos/modules/config/update-users-groups.pl
@@ -186,7 +186,7 @@ foreach my $name (keys %groupsCur) {
 # Rewrite /etc/group. FIXME: acquire lock.
 my @lines = map { join(":", $_->{name}, $_->{password}, $_->{gid}, $_->{members}) . "\n" }
     (sort { $a->{gid} <=> $b->{gid} } values(%groupsOut));
-updateFile($gidMapFile, to_json($gidMap));
+updateFile($gidMapFile, to_json($gidMap, {canonical => 1}));
 updateFile("/etc/group", \@lines);
 nscdInvalidate("group");
 
@@ -272,7 +272,7 @@ foreach my $name (keys %usersCur) {
 # Rewrite /etc/passwd. FIXME: acquire lock.
 @lines = map { join(":", $_->{name}, $_->{fakePassword}, $_->{uid}, $_->{gid}, $_->{description}, $_->{home}, $_->{shell}) . "\n" }
     (sort { $a->{uid} <=> $b->{uid} } (values %usersOut));
-updateFile($uidMapFile, to_json($uidMap));
+updateFile($uidMapFile, to_json($uidMap, {canonical => 1}));
 updateFile("/etc/passwd", \@lines);
 nscdInvalidate("passwd");