diff --git a/modules/installer/tools/nixos-rebuild.sh b/modules/installer/tools/nixos-rebuild.sh
index 255c8150bdde..fb26279e7c7f 100644
--- a/modules/installer/tools/nixos-rebuild.sh
+++ b/modules/installer/tools/nixos-rebuild.sh
@@ -191,9 +191,6 @@ fi
 # If we're not just building, then make the new configuration the boot
 # default and/or activate it now.
 if [ "$action" = switch -o "$action" = boot -o "$action" = test ]; then
-    # Just in case the new configuration hangs the system, do a sync now.
-    sync
-
     $pathToConfig/bin/switch-to-configuration "$action"
 fi
 
diff --git a/modules/system/activation/switch-to-configuration.pl b/modules/system/activation/switch-to-configuration.pl
index a95ebcaba249..4db53c9043ec 100644
--- a/modules/system/activation/switch-to-configuration.pl
+++ b/modules/system/activation/switch-to-configuration.pl
@@ -33,9 +33,13 @@ openlog("nixos", "", LOG_USER);
 # Install or update the bootloader.
 if ($action eq "switch" || $action eq "boot") {
     system("@installBootLoader@ $out") == 0 or exit 1;
-    exit 0 if $action eq "boot";
 }
 
+# Just in case the new configuration hangs the system, do a sync now.
+system("sync") unless ($ENV{"NIXOS_NO_SYNC"} // "") eq "1";
+
+exit 0 if $action eq "boot";
+
 # Check if we can activate the new configuration.
 my $oldVersion = read_file("/run/current-system/init-interface-version", err_mode => 'quiet') // "";
 my $newVersion = read_file("$out/init-interface-version");