diff --git a/nixos/modules/system/activation/switch-to-configuration.pl b/nixos/modules/system/activation/switch-to-configuration.pl
index 88e7847cf8c8..29cc60b00324 100644
--- a/nixos/modules/system/activation/switch-to-configuration.pl
+++ b/nixos/modules/system/activation/switch-to-configuration.pl
@@ -147,11 +147,16 @@ my $activePrev = getActiveUnits;
 while (my ($unit, $state) = each %{$activePrev}) {
     my $baseUnit = $unit;
 
-    # Recognise template instances.
-    $baseUnit = "$1\@.$2" if $unit =~ /^(.*)@[^\.]*\.(.*)$/;
     my $prevUnitFile = "/etc/systemd/system/$baseUnit";
     my $newUnitFile = "$out/etc/systemd/system/$baseUnit";
 
+    # Detect template instances.
+    if (!-e $prevUnitFile && !-e $newUnitFile && $unit =~ /^(.*)@[^\.]*\.(.*)$/) {
+      $baseUnit = "$1\@.$2";
+      $prevUnitFile = "/etc/systemd/system/$baseUnit";
+      $newUnitFile = "$out/etc/systemd/system/$baseUnit";
+    }
+
     my $baseName = $baseUnit;
     $baseName =~ s/\.[a-z]*$//;