diff --git a/.changeset/quiet-lions-batch.md b/.changeset/quiet-lions-batch.md
new file mode 100644
index 0000000..a5f617c
--- /dev/null
+++ b/.changeset/quiet-lions-batch.md
@@ -0,0 +1,5 @@
+---
+'posthog-php': patch
+---
+
+Keep the default batch size when invalid non-positive values are configured.
diff --git a/lib/QueueConsumer.php b/lib/QueueConsumer.php
index e45f7e8..b1fa52e 100644
--- a/lib/QueueConsumer.php
+++ b/lib/QueueConsumer.php
@@ -34,8 +34,8 @@ public function __construct($apiKey, $options = array())
             $this->max_queue_size = $options["max_queue_size"];
         }
 
-        if (isset($options["batch_size"])) {
-            $this->batch_size = $options["batch_size"];
+        if (isset($options["batch_size"]) && (int) $options["batch_size"] > 0) {
+            $this->batch_size = (int) $options["batch_size"];
         }
 
         if (isset($options["maximum_backoff_duration"])) {
diff --git a/test/PostHogTest.php b/test/PostHogTest.php
index f52bb95..abbe64c 100644
--- a/test/PostHogTest.php
+++ b/test/PostHogTest.php
@@ -101,6 +101,15 @@ public static function disabledClientNoRequestCases(): array
         ];
     }
 
+    public static function queuedBatchSizeCases(): array
+    {
+        return [
+            'default' => [["debug" => true]],
+            'zero' => [["debug" => true, "batch_size" => 0]],
+            'negative' => [["debug" => true, "batch_size" => -1]],
+        ];
+    }
+
     public static function facadeNoOpBeforeInitCases(): array
     {
         return [
@@ -368,6 +377,45 @@ public function testClientWithBlankApiKeyDoesNotSendRequests(?string $apiKey, st
         $this->assertSame([], $httpClient->calls ?? []);
     }
 
+    /**
+     * @dataProvider queuedBatchSizeCases
+     */
+    public function testCapturesStayQueuedUntilFlush(array $options): void
+    {
+        $httpClient = new MockedHttpClient("app.posthog.com");
+        $client = new Client(self::FAKE_API_KEY, $options, $httpClient, null, false);
+
+        $this->assertTrue($client->capture([
+            "distinctId" => "john",
+            "event" => "Module PHP Event",
+        ]));
+        $this->assertSame(0, count($httpClient->calls ?? []));
+
+        $this->assertTrue($client->flush());
+        $this->assertSame(1, count($httpClient->calls ?? []));
+        $this->assertSame('/batch/', $httpClient->calls[0]['path']);
+    }
+
+    public function testBatchSizeOneFlushesImmediately(): void
+    {
+        $httpClient = new MockedHttpClient("app.posthog.com");
+        $client = new Client(
+            self::FAKE_API_KEY,
+            ["debug" => true, "batch_size" => 1],
+            $httpClient,
+            null,
+            false
+        );
+
+        $this->assertTrue($client->capture([
+            "distinctId" => "john",
+            "event" => "Module PHP Event",
+        ]));
+        $this->assertSame(1, count($httpClient->calls ?? []));
+        $this->assertSame('/batch/', $httpClient->calls[0]['path']);
+    }
+
+
     /**
      * @dataProvider facadeNoOpBeforeInitCases
      */