diff --git a/lib/CleantalkSP/SpbctWP/Sync.php b/lib/CleantalkSP/SpbctWP/Sync.php
index 58dd25553..4c73fcba1 100644
--- a/lib/CleantalkSP/SpbctWP/Sync.php
+++ b/lib/CleantalkSP/SpbctWP/Sync.php
@@ -25,6 +25,14 @@ class Sync
         'finalize'            => 'Sync end...',
     );
 
+    private const MODE_SYNC       = 'sync';
+    private const MODE_BACKGROUND = 'background';
+
+    /**
+     * Seconds without step progress after which a synchronous sync is considered dead.
+     */
+    private const SYNC_MODE_STALE_TIMEOUT = 300;
+
     /**
      * @return array<string, mixed>
      */
@@ -32,6 +40,7 @@ private static function getDefaultProgress()
     {
         return array(
             'in_progress'   => false,
+            'mode'          => '',
             'step_index'    => 0,
             'account_is_ok' => false,
             'message'       => '',
@@ -91,32 +100,18 @@ public static function formatStatus($progress)
      */
     public static function run()
     {
-        global $spbc;
+        // Sync mode turns queued background continuations and status polling into no-ops.
+        self::initializeProgress(self::MODE_SYNC);
 
-        $progress = self::getProgress();
-        if ( ! empty($progress['in_progress']) ) {
-            self::saveProgress(self::getDefaultProgress());
-        }
-
-        $account_is_ok = false;
+        do {
+            self::runCurrentStep();
+            $progress = self::getProgress();
+        } while ( ! empty($progress['in_progress']) );
 
-        self::stepAccessKeyCheck($account_is_ok);
-        self::stepSecfwUpdate($account_is_ok);
-        self::stepSignaturesUpdate();
-        self::stepSettingsExclusions();
-        self::stepAdjustEnv();
-        self::stepVulnerabilityCheck();
-        self::stepAnalysisLogUpdate($account_is_ok);
-        self::stepPscCacheWarm();
-
-        $out = array(
-            'success' => true,
-            'reload'  => self::needsReloadPage($spbc),
+        return array(
+            'success' => ! empty($progress['success']),
+            'reload'  => ! empty($progress['reload']),
         );
-
-        self::stepFinalize();
-
-        return $out;
     }
 
     /**
@@ -193,12 +188,13 @@ public static function runCurrentStep()
                 self::stepPscCacheWarm();
                 break;
             case 'finalize':
+                $reload = self::needsReloadPage($spbc);
                 self::stepFinalize();
 
                 $progress                 = self::getProgress();
                 $progress['in_progress']  = false;
                 $progress['success']      = true;
-                $progress['reload']       = self::needsReloadPage($spbc);
+                $progress['reload']       = $reload;
                 $progress['percent']      = 100;
                 $progress['message']      = self::STEPS['finalize'];
                 $progress['last_step_at'] = time();
@@ -241,6 +237,16 @@ public static function maybeResume()
             return;
         }
 
+        if ( $progress['mode'] === self::MODE_SYNC ) {
+            // Synchronous sync is running in another process. Take it over only if that process has died.
+            if ( time() - (int) $progress['last_step_at'] < self::SYNC_MODE_STALE_TIMEOUT ) {
+                return;
+            }
+
+            $progress['mode'] = self::MODE_BACKGROUND;
+            self::saveProgress($progress);
+        }
+
         $steps = array_keys(self::STEPS);
         if ( (int) $progress['step_index'] >= count($steps) ) {
             return;
@@ -276,20 +282,7 @@ public static function startBackground()
             return self::formatStatus(self::getProgress());
         }
 
-        $steps  = array_keys(self::STEPS);
-        $labels = self::STEPS;
-
-        $progress = array(
-            'in_progress'   => true,
-            'step_index'    => 0,
-            'account_is_ok' => false,
-            'message'       => $labels[ $steps[0] ],
-            'percent'       => 0,
-            'reload'        => false,
-            'success'       => false,
-            'last_step_at'  => time(),
-        );
-        self::saveProgress($progress);
+        self::initializeProgress(self::MODE_BACKGROUND);
 
         self::runCurrentStep();
 
@@ -301,11 +294,31 @@ public static function startBackground()
         return self::formatStatus(self::getProgress());
     }
 
+    /**
+     * Initialize progress for synchronous and background sync.
+     *
+     * @param string $mode self::MODE_SYNC or self::MODE_BACKGROUND
+     */
+    private static function initializeProgress($mode)
+    {
+        $progress = self::getDefaultProgress();
+        $progress['in_progress']  = true;
+        $progress['mode']         = $mode;
+        $progress['message']      = self::STEPS['access_key_check'];
+        $progress['last_step_at'] = time();
+        self::saveProgress($progress);
+    }
+
     /**
      * Remote call handler: run the next sync step.
      */
     public static function continueSync()
     {
+        $progress = self::getProgress();
+        if ( $progress['mode'] === self::MODE_SYNC ) {
+            return;
+        }
+
         self::runCurrentStep();
 
         $progress = self::getProgress();