diff --git a/modules/services/networking/dhcpcd.nix b/modules/services/networking/dhcpcd.nix
index 2a0d73f6004..cf7f621a85d 100644
--- a/modules/services/networking/dhcpcd.nix
+++ b/modules/services/networking/dhcpcd.nix
@@ -97,6 +97,11 @@ in
 
         wantedBy = [ "network.target" ];
 
+        # Stopping dhcpcd during a reconfiguration is undesirable
+        # because it brings down the network interfaces configured by
+        # dhcpcd.  So do a "systemctl restart" instead.
+        stopIfChanged = false;
+
         path = [ dhcpcd pkgs.nettools pkgs.openresolv ];
 
         serviceConfig =
diff --git a/modules/services/networking/ssh/sshd.nix b/modules/services/networking/ssh/sshd.nix
index 21f81152fa5..8f898ce06a1 100644
--- a/modules/services/networking/ssh/sshd.nix
+++ b/modules/services/networking/ssh/sshd.nix
@@ -267,6 +267,8 @@ in
 
         wantedBy = [ "multi-user.target" ];
 
+        stopIfChanged = false;
+
         path = [ pkgs.openssh ];
 
         environment.LD_LIBRARY_PATH = nssModulesPath;
diff --git a/modules/system/activation/switch-to-configuration.pl b/modules/system/activation/switch-to-configuration.pl
index b085778f099..28ccc158f72 100644
--- a/modules/system/activation/switch-to-configuration.pl
+++ b/modules/system/activation/switch-to-configuration.pl
@@ -6,6 +6,7 @@ use File::Basename;
 use File::Slurp;
 use Cwd 'abs_path';
 
+my $startListFile = "/run/systemd/start-list";
 my $restartListFile = "/run/systemd/restart-list";
 my $reloadListFile = "/run/systemd/reload-list";
 
@@ -125,7 +126,7 @@ while (my ($unit, $state) = each %{$activePrev}) {
             if ($unit ne "suspend.target" && $unit ne "hibernate.target") {
                 my $unitInfo = parseUnit($newUnitFile);
                 unless (boolIsTrue($unitInfo->{'RefuseManualStart'} // "false")) {
-                    write_file($restartListFile, { append => 1 }, "$unit\n");
+                    write_file($startListFile, { append => 1 }, "$unit\n");
                 }
             }
         }
@@ -158,21 +159,31 @@ while (my ($unit, $state) = each %{$activePrev}) {
                         foreach my $socket (@sockets) {
                             if (defined $activePrev->{$socket}) {
                                 push @unitsToStop, $socket;
-                                write_file($restartListFile, { append => 1 }, "$socket\n");
+                                write_file($startListFile, { append => 1 }, "$socket\n");
                                 $socketActivated = 1;
                             }
                         }
                     }
 
-                    # Otherwise, record that this unit needs to be
-                    # started below.  We write this to a file to
-                    # ensure that the service gets restarted if we're
-                    # interrupted.
-                    if (!$socketActivated) {
-                        write_file($restartListFile, { append => 1 }, "$unit\n");
-                    }
+                    if (!boolIsTrue($unitInfo->{'X-StopIfChanged'} // "true")) {
 
-                    push @unitsToStop, $unit;
+                        # This unit should be restarted instead of
+                        # stopped and started.
+                        write_file($restartListFile, { append => 1 }, "$unit\n");
+
+                    } else {
+
+                        # If the unit is not socket-activated, record
+                        # that this unit needs to be started below.
+                        # We write this to a file to ensure that the
+                        # service gets restarted if we're interrupted.
+                        if (!$socketActivated) {
+                            write_file($startListFile, { append => 1 }, "$unit\n");
+                        }
+
+                        push @unitsToStop, $unit;
+
+                    }
                 }
             }
         }
@@ -216,7 +227,7 @@ foreach my $mountPoint (keys %$prevFss) {
         push @unitsToStop, $unit;
     } elsif ($prev->{fsType} ne $new->{fsType} || $prev->{device} ne $new->{device}) {
         # Filesystem type or device changed, so unmount and mount it.
-        write_file($restartListFile, { append => 1 }, "$unit\n");
+        write_file($startListFile, { append => 1 }, "$unit\n");
         push @unitsToStop, $unit;
     } elsif ($prev->{options} ne $new->{options}) {
         # Mount options changes, so remount it.
@@ -266,16 +277,25 @@ system("@systemd@/bin/systemctl", "reset-failed");
 # Make systemd reload its units.
 system("@systemd@/bin/systemctl", "daemon-reload") == 0 or $res = 3;
 
+# Restart changed services (those that have to be restarted rather
+# than stopped and started).
+my @restart = unique(split('\n', read_file($restartListFile, err_mode => 'quiet') // ""));
+if (scalar @restart > 0) {
+    print STDERR "restarting the following units: ", join(", ", sort(@restart)), "\n";
+    system("@systemd@/bin/systemctl", "restart", "--", @restart) == 0 or $res = 4;
+    unlink($restartListFile);
+}
+
 # Start all active targets, as well as changed units we stopped above.
 # The latter is necessary because some may not be dependencies of the
 # targets (i.e., they were manually started).  FIXME: detect units
 # that are symlinks to other units.  We shouldn't start both at the
 # same time because we'll get a "Failed to add path to set" error from
 # systemd.
-my @start = unique("default.target", split('\n', read_file($restartListFile, err_mode => 'quiet') // ""));
+my @start = unique("default.target", split('\n', read_file($startListFile, err_mode => 'quiet') // ""));
 print STDERR "starting the following units: ", join(", ", sort(@start)), "\n";
 system("@systemd@/bin/systemctl", "start", "--", @start) == 0 or $res = 4;
-unlink($restartListFile);
+unlink($startListFile);
 
 # Reload units that need it.  This includes remounting changed mount
 # units.
diff --git a/modules/system/boot/systemd-unit-options.nix b/modules/system/boot/systemd-unit-options.nix
index ad9b5da2316..1f8097ada1c 100644
--- a/modules/system/boot/systemd-unit-options.nix
+++ b/modules/system/boot/systemd-unit-options.nix
@@ -183,6 +183,21 @@ rec {
       '';
     };
 
+    stopIfChanged = mkOption {
+      type = types.bool;
+      default = true;
+      description = ''
+        If set, a changed unit is restarted by calling
+        <command>systemctl stop</command> in the old configuration,
+        then <command>systemctl start</command> in the new one.
+        Otherwise, it is restarted in a single step using
+        <command>systemctl restart</command> in the new configuration.
+        The latter is less correct because it runs the
+        <literal>ExecStop</literal> commands from the new
+        configuration.
+      '';
+    };
+
   };
 
 
diff --git a/modules/system/boot/systemd.nix b/modules/system/boot/systemd.nix
index f4d0655118e..a0462951d00 100644
--- a/modules/system/boot/systemd.nix
+++ b/modules/system/boot/systemd.nix
@@ -246,6 +246,7 @@ let
           ${let env = cfg.globalEnvironment // def.environment;
             in concatMapStrings (n: "Environment=${n}=${getAttr n env}\n") (attrNames env)}
           ${optionalString (!def.restartIfChanged) "X-RestartIfChanged=false"}
+          ${optionalString (!def.stopIfChanged) "X-StopIfChanged=false"}
 
           ${optionalString (def.preStart != "") ''
             ExecStartPre=${makeJobScript "${name}-pre-start" ''