diff --git a/tests/SpecTests/RetryableWritesSpecTest.php b/tests/SpecTests/RetryableWritesSpecTest.php
index b85eb1c27..7752942e5 100644
--- a/tests/SpecTests/RetryableWritesSpecTest.php
+++ b/tests/SpecTests/RetryableWritesSpecTest.php
@@ -34,12 +34,15 @@ class RetryableWritesSpecTest extends FunctionalTestCase
      */
     public function testRetryableWrites(stdClass $test, ?array $runOn, array $data): void
     {
-        $useMultipleMongoses = isset($test->useMultipleMongoses) && $test->useMultipleMongoses && $this->isMongos();
-
         if (isset($runOn)) {
             $this->checkServerRequirements($runOn);
         }
 
+        // Serverless uses a load balancer fronting a single proxy (PHPLIB-757)
+        $useMultipleMongoses = ($this->isMongos() || ($this->isLoadBalanced() && ! $this->isServerless()))
+            ? ($test->useMultipleMongoses ?? false)
+            : false;
+
         $context = Context::fromRetryableWrites($test, $this->getDatabaseName(), $this->getCollectionName(), $useMultipleMongoses);
         $this->setContext($context);
 
diff --git a/tests/SpecTests/TransactionsSpecTest.php b/tests/SpecTests/TransactionsSpecTest.php
index 226ece4ae..fb89efad3 100644
--- a/tests/SpecTests/TransactionsSpecTest.php
+++ b/tests/SpecTests/TransactionsSpecTest.php
@@ -143,8 +143,6 @@ private function runTransactionTest(stdClass $test, ?array $runOn, array $data,
             $this->markTestIncomplete(self::$incompleteTests[$this->dataDescription()]);
         }
 
-        $useMultipleMongoses = isset($test->useMultipleMongoses) && $test->useMultipleMongoses && $this->isMongos();
-
         if (isset($runOn)) {
             $this->checkServerRequirements($runOn);
         }
@@ -156,6 +154,11 @@ private function runTransactionTest(stdClass $test, ?array $runOn, array $data,
         $databaseName ??= $this->getDatabaseName();
         $collectionName ??= $this->getCollectionName();
 
+        // Serverless uses a load balancer fronting a single proxy (PHPLIB-757)
+        $useMultipleMongoses = ($this->isMongos() || ($this->isLoadBalanced() && ! $this->isServerless()))
+            ? ($test->useMultipleMongoses ?? false)
+            : false;
+
         $context = Context::fromTransactions($test, $databaseName, $collectionName, $useMultipleMongoses);
         $this->setContext($context);