diff --git a/src/ApplicationDefaultCredentials.php b/src/ApplicationDefaultCredentials.php
index edfd6d6c2..732dd8b6e 100644
--- a/src/ApplicationDefaultCredentials.php
+++ b/src/ApplicationDefaultCredentials.php
@@ -72,7 +72,7 @@
  */
 class ApplicationDefaultCredentials
 {
-    private const SDK_DEBUG_FLAG = 'GOOGLE_SDK_DEBUG_LOGGING';
+    private const SDK_DEBUG_FLAG = 'GOOGLE_SDK_PHP_LOGGING';
 
     /**
      * @deprecated
diff --git a/tests/ApplicationDefaultCredentialsTest.php b/tests/ApplicationDefaultCredentialsTest.php
index 6d6851f9a..5c1936b53 100644
--- a/tests/ApplicationDefaultCredentialsTest.php
+++ b/tests/ApplicationDefaultCredentialsTest.php
@@ -49,7 +49,7 @@ class ApplicationDefaultCredentialsTest extends TestCase
     private $targetAudience = 'a target audience';
     private $quotaProject = 'a-quota-project';
     private $originalServiceAccount;
-    private const SDK_DEBUG_FLAG = 'GOOGLE_SDK_DEBUG_LOGGING';
+    private const SDK_DEBUG_FLAG = 'GOOGLE_SDK_PHP_LOGGING';
 
     public function testGetCredentialsFailsIfEnvSpecifiesNonExistentFile()
     {