diff --git a/_config.php b/_config.php
index a372c88..ec27655 100644
--- a/_config.php
+++ b/_config.php
@@ -12,7 +12,7 @@
  */
 if (class_exists('Resque_Event') && class_exists('SSResqueRun')) {
     Resque_Event::listen('beforeFork', function ($data) {
-        $databaseConfig = DB::getConfig();
+        $databaseConfig = DB::getConfig(DB::CONN_PRIMARY);
 
         // Reconnect to the database - this may connect to the old DB first, but is required because these processes
         // are long-lived, and MySQL connections often get closed in between worker runs. We need to connect before
diff --git a/src/TestSessionEnvironment.php b/src/TestSessionEnvironment.php
index dcd1405..99b09d7 100644
--- a/src/TestSessionEnvironment.php
+++ b/src/TestSessionEnvironment.php
@@ -271,7 +271,7 @@ public function applyState($state)
         $this->extend('onBeforeApplyState', $state);
 
         // back up source
-        $databaseConfig = DB::getConfig();
+        $databaseConfig = DB::getConfig(DB::CONN_PRIMARY);
         $this->oldDatabaseName = $databaseConfig['database'];
 
         // Load existing state from $this->state into $state, if there is any
@@ -514,9 +514,9 @@ public function loadFixtureIntoDb($fixtureFile)
     public function resetDatabaseName()
     {
         if ($this->oldDatabaseName) {
-            $databaseConfig = DB::getConfig();
+            $databaseConfig = DB::getConfig(DB::CONN_PRIMARY);
             $databaseConfig['database'] = $this->oldDatabaseName;
-            DB::setConfig($databaseConfig);
+            DB::setConfig($databaseConfig, DB::CONN_PRIMARY);
 
             $conn = DB::get_conn();
 
@@ -559,7 +559,7 @@ public function connectToDatabase($state = null)
             $state = $this->getState();
         }
 
-        $databaseConfig = DB::getConfig();
+        $databaseConfig = DB::getConfig(DB::CONN_PRIMARY);
 
         if (isset($state->database) && $state->database) {
             if (!DB::get_conn()) {
@@ -570,14 +570,14 @@ public function connectToDatabase($state = null)
                 }
 
                 // Connect to database
-                DB::connect($databaseConfig);
+                $this->connectToDB($databaseConfig);
             } else {
                 // We've already connected to the database, do a fast check to see what database we're currently using
                 $db = DB::get_conn()->getSelectedDatabase();
                 if (isset($state->database) && $db != $state->database) {
                     $this->oldDatabaseName = $databaseConfig['database'];
                     $databaseConfig['database'] = $state->database;
-                    DB::connect($databaseConfig);
+                    $this->connectToDB($databaseConfig);
                 }
             }
         }
@@ -613,4 +613,17 @@ public function waitForPendingRequests($await = 700, $timeout = 10000)
 
         return true;
     }
+
+    private function connectToDB(array $databaseConfig): void
+    {
+        if (method_exists(DB::class, 'hasConfig')) {
+            // CMS 5.4+ - ensure we connect the primary connection and not a replica
+            // which can happen if we use the default value of DB::CONN_DYNAMIC
+            // and there is a replica database configured
+            DB::connect($databaseConfig, DB::CONN_PRIMARY);
+        } else {
+            // CMS 5.3 and below do not support replica connections, use 'default' connection
+            DB::connect($databaseConfig);
+        }
+    }
 }