diff --git a/modules/installer/tools/nixos-install.sh b/modules/installer/tools/nixos-install.sh
index 5937883b86b..13b62b5dc7f 100644
--- a/modules/installer/tools/nixos-install.sh
+++ b/modules/installer/tools/nixos-install.sh
@@ -80,7 +80,7 @@ mkdir -m 0755 -p \
     $mountPoint/nix/var/log/nix/drvs
 
 mkdir -m 1775 -p $mountPoint/nix/store
-chown root.nixbld $mountPoint/nix/store
+chown root:nixbld $mountPoint/nix/store
 
 
 # Get the store paths to copy from the references graph.
diff --git a/modules/security/policykit.nix b/modules/security/policykit.nix
index 0d56a519e81..5aa02950f74 100644
--- a/modules/security/policykit.nix
+++ b/modules/security/policykit.nix
@@ -64,15 +64,15 @@ in
     system.activationScripts.policyKit = stringAfter [ "users" ]
       ''
         mkdir -m 0770 -p /var/run/PolicyKit
-        chown root.polkituser /var/run/PolicyKit
+        chown root:polkituser /var/run/PolicyKit
 
         mkdir -m 0770 -p /var/lib/PolicyKit
-        chown root.polkituser /var/lib/PolicyKit
+        chown root:polkituser /var/lib/PolicyKit
 
         mkdir -p /var/lib/misc
         touch /var/lib/misc/PolicyKit.reload
         chmod 0664 /var/lib/misc/PolicyKit.reload
-        chown polkituser.polkituser /var/lib/misc/PolicyKit.reload
+        chown polkituser:polkituser /var/lib/misc/PolicyKit.reload
       '';
 
   };
diff --git a/modules/services/mail/dovecot.nix b/modules/services/mail/dovecot.nix
index 4c6ee85ac31..ff41c8f4302 100644
--- a/modules/services/mail/dovecot.nix
+++ b/modules/services/mail/dovecot.nix
@@ -119,7 +119,7 @@ in
         preStart =
           ''
             ${pkgs.coreutils}/bin/mkdir -p /var/run/dovecot /var/run/dovecot/login
-            ${pkgs.coreutils}/bin/chown -R ${cfg.user}.${cfg.group} /var/run/dovecot
+            ${pkgs.coreutils}/bin/chown -R ${cfg.user}:${cfg.group} /var/run/dovecot
           '';
 
         exec = "${pkgs.dovecot}/sbin/dovecot -F -c ${confFile}";
diff --git a/modules/services/mail/dovecot2.nix b/modules/services/mail/dovecot2.nix
index 15a0ecce325..c7ae59afa20 100644
--- a/modules/services/mail/dovecot2.nix
+++ b/modules/services/mail/dovecot2.nix
@@ -128,7 +128,7 @@ in
         preStart =
           ''
             ${pkgs.coreutils}/bin/mkdir -p /var/run/dovecot2 /var/run/dovecot2/login
-            ${pkgs.coreutils}/bin/chown -R ${cfg.user}.${cfg.group} /var/run/dovecot2
+            ${pkgs.coreutils}/bin/chown -R ${cfg.user}:${cfg.group} /var/run/dovecot2
           '';
 
         exec = "${pkgs.dovecot_2_0}/sbin/dovecot -F -c ${confFile}";
diff --git a/modules/services/mail/postfix.nix b/modules/services/mail/postfix.nix
index f98c9e6b0a7..d4314236a9b 100644
--- a/modules/services/mail/postfix.nix
+++ b/modules/services/mail/postfix.nix
@@ -329,10 +329,10 @@ in
               ${pkgs.coreutils}/bin/mkdir -p /var/spool/mail /var/postfix/conf /var/postfix/queue
             fi
 
-            ${pkgs.coreutils}/bin/chown -R ${user}.${group} /var/postfix
-            ${pkgs.coreutils}/bin/chown -R ${user}.${setgidGroup} /var/postfix/queue
+            ${pkgs.coreutils}/bin/chown -R ${user}:${group} /var/postfix
+            ${pkgs.coreutils}/bin/chown -R ${user}:${setgidGroup} /var/postfix/queue
             ${pkgs.coreutils}/bin/chmod -R ug+rwX /var/postfix/queue
-            ${pkgs.coreutils}/bin/chown root.root /var/spool/mail
+            ${pkgs.coreutils}/bin/chown root:root /var/spool/mail
             ${pkgs.coreutils}/bin/chmod a+rwxt /var/spool/mail
 
             ln -sf ${pkgs.postfix}/share/postfix/conf/* /var/postfix/conf
diff --git a/modules/services/misc/nix-daemon.nix b/modules/services/misc/nix-daemon.nix
index 7c4da0c9405..31b81a13e36 100644
--- a/modules/services/misc/nix-daemon.nix
+++ b/modules/services/misc/nix-daemon.nix
@@ -301,7 +301,7 @@ in
     system.activationScripts.nix = stringAfter [ "etc" "users" ]
       ''
         # Set up Nix.
-        chown root.nixbld /nix/store
+        chown root:nixbld /nix/store
         chmod 1775 /nix/store
 
         # Nix initialisation.
diff --git a/modules/services/monitoring/systemhealth.nix b/modules/services/monitoring/systemhealth.nix
index cb46ba89bc9..71389be5b2f 100644
--- a/modules/services/monitoring/systemhealth.nix
+++ b/modules/services/monitoring/systemhealth.nix
@@ -80,7 +80,7 @@ in
     system.activationScripts.systemhealth = stringAfter [ "var" ]
       ''
         mkdir -p ${rrdDir} ${htmlDir}
-        chown wwwrun.wwwrun ${rrdDir} ${htmlDir}
+        chown wwwrun:wwwrun ${rrdDir} ${htmlDir}
 
         cat >${configFile} << EOF
         [paths]
@@ -110,7 +110,7 @@ in
 
         EOF
 
-        chown wwwrun.wwwrun ${configFile}
+        chown wwwrun:wwwrun ${configFile}
 
         ${pkgs.su}/bin/su -s "/bin/sh" -c "${command} --check" wwwrun
         ${pkgs.su}/bin/su -s "/bin/sh" -c "${command} --html" wwwrun