diff --git a/src/helpers/Api.php b/src/helpers/Api.php
index ef5e68d4592..b04d0792489 100644
--- a/src/helpers/Api.php
+++ b/src/helpers/Api.php
@@ -204,7 +204,7 @@ public static function processResponseHeaders(array $headers): void
 
         // did we just get any new plugin license keys?
         $pluginsService = Craft::$app->getPlugins();
-        if (isset($headers['x-craft-plugin-licenses'])) {
+        if (isset($headers['x-craft-plugin-licenses']) && !Craft::$app->getProjectConfig()->readOnly) {
             $pluginLicenseKeys = explode(',', reset($headers['x-craft-plugin-licenses']));
             foreach ($pluginLicenseKeys as $key) {
                 [$pluginHandle, $key] = explode(':', $key);
diff --git a/tests/unit/helpers/ApiHelperTest.php b/tests/unit/helpers/ApiHelperTest.php
index cbb184be318..d4a8764d2db 100644
--- a/tests/unit/helpers/ApiHelperTest.php
+++ b/tests/unit/helpers/ApiHelperTest.php
@@ -10,6 +10,7 @@
 use Craft;
 use craft\helpers\Api;
 use craft\helpers\App;
+use craft\services\Plugins;
 use craft\test\TestCase;
 
 /**
@@ -79,6 +80,97 @@ public function testLicenseInfo(): void
         self::assertNull($licenseInfo['plugin-invalid']['id']);
     }
 
+    public function testPluginLicenseWriteIsSkippedWhenProjectConfigIsReadOnly(): void
+    {
+        $cache = Craft::$app->getCache();
+
+        $projectConfig = Craft::$app->getProjectConfig();
+        $readOnly = $projectConfig->readOnly;
+        $plugins = Craft::$app->getPlugins();
+
+        try {
+            $projectConfig->readOnly = true;
+            $pluginsMock = $this->createMock(Plugins::class);
+            $pluginsMock->expects(self::never())
+                ->method('setPluginLicenseKey');
+            Craft::$app->set('plugins', $pluginsMock);
+
+            Api::processResponseHeaders([
+                'X-Craft-Plugin-Licenses' => 'example-plugin:license-key',
+                'X-Craft-License-Info' => 'plugin-example-plugin:123;standard;valid',
+            ]);
+
+            $licenseInfo = $cache->get(App::CACHE_KEY_LICENSE_INFO);
+            self::assertSame('123', $licenseInfo['plugin-example-plugin']['id']);
+            self::assertSame('standard', $licenseInfo['plugin-example-plugin']['edition']);
+            self::assertSame('valid', $licenseInfo['plugin-example-plugin']['status']);
+        } finally {
+            Craft::$app->set('plugins', $plugins);
+            $projectConfig->readOnly = $readOnly;
+        }
+    }
+
+    public function testPluginLicenseWriteOccursWhenProjectConfigIsWritable(): void
+    {
+        $projectConfig = Craft::$app->getProjectConfig();
+        $readOnly = $projectConfig->readOnly;
+        $plugins = Craft::$app->getPlugins();
+
+        try {
+            $projectConfig->readOnly = false;
+            $pluginsMock = $this->createMock(Plugins::class);
+            $pluginsMock->expects(self::once())
+                ->method('setPluginLicenseKey')
+                ->with('example-plugin', 'license-key')
+                ->willReturn(true);
+            Craft::$app->set('plugins', $pluginsMock);
+
+            Api::processResponseHeaders([
+                'X-Craft-Plugin-Licenses' => 'example-plugin:license-key',
+            ]);
+        } finally {
+            Craft::$app->set('plugins', $plugins);
+            $projectConfig->readOnly = $readOnly;
+        }
+    }
+
+    /**
+     * @dataProvider projectConfigReadOnlyDataProvider
+     */
+    public function testResponseWithoutPluginLicensesDoesNotWritePluginLicense(bool $readOnly): void
+    {
+        $cache = Craft::$app->getCache();
+
+        $projectConfig = Craft::$app->getProjectConfig();
+        $originalReadOnly = $projectConfig->readOnly;
+        $plugins = Craft::$app->getPlugins();
+
+        try {
+            $projectConfig->readOnly = $readOnly;
+            $pluginsMock = $this->createMock(Plugins::class);
+            $pluginsMock->expects(self::never())
+                ->method('setPluginLicenseKey');
+            Craft::$app->set('plugins', $pluginsMock);
+
+            Api::processResponseHeaders([
+                'X-Craft-License-Domain' => 'example.test',
+            ]);
+
+            self::assertSame('example.test', $cache->get('licensedDomain'));
+        } finally {
+            Craft::$app->set('plugins', $plugins);
+            $projectConfig->readOnly = $originalReadOnly;
+        }
+    }
+
+    public static function projectConfigReadOnlyDataProvider(): array
+    {
+        return [
+            [false],
+            [true],
+        ];
+    }
+
     protected function _before(): void
     {
         parent::_before();