diff --git a/google-auth-library-java/oauth2_http/java/com/google/auth/oauth2/ComputeEngineCredentials.java b/google-auth-library-java/oauth2_http/java/com/google/auth/oauth2/ComputeEngineCredentials.java
index bcfe916c3168..eff14ea47b40 100644
--- a/google-auth-library-java/oauth2_http/java/com/google/auth/oauth2/ComputeEngineCredentials.java
+++ b/google-auth-library-java/oauth2_http/java/com/google/auth/oauth2/ComputeEngineCredentials.java
@@ -800,8 +800,20 @@ public String getAccount() {
   @InternalApi
   @Override
   public String getRegionalAccessBoundaryUrl() throws IOException {
+    String account = getAccount();
+    // In GKE environments, the default service account might return a non-email placeholder.
+    // Since RAB lookup requires a valid email-based service account, we skip RAB lookup
+    // in non-email scenarios by returning null.
+    if (account == null || !account.contains("@")) {
+      LoggingUtils.log(
+          LOGGER_PROVIDER,
+          Level.INFO,
+          Collections.emptyMap(),
+          "Regional Access Boundary lookup is skipped for this instance because it is a non-email instance.");
+      return null;
+    }
     return String.format(
-        OAuth2Utils.IAM_CREDENTIALS_ALLOWED_LOCATIONS_URL_FORMAT_SERVICE_ACCOUNT, getAccount());
+        OAuth2Utils.IAM_CREDENTIALS_ALLOWED_LOCATIONS_URL_FORMAT_SERVICE_ACCOUNT, account);
   }
 
   /**
diff --git a/google-auth-library-java/oauth2_http/java/com/google/auth/oauth2/RegionalAccessBoundaryManager.java b/google-auth-library-java/oauth2_http/java/com/google/auth/oauth2/RegionalAccessBoundaryManager.java
index e35efe86f7a0..683015614782 100644
--- a/google-auth-library-java/oauth2_http/java/com/google/auth/oauth2/RegionalAccessBoundaryManager.java
+++ b/google-auth-library-java/oauth2_http/java/com/google/auth/oauth2/RegionalAccessBoundaryManager.java
@@ -42,6 +42,7 @@
 import java.util.concurrent.LinkedBlockingQueue;
 import java.util.concurrent.ThreadPoolExecutor;
 import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.concurrent.atomic.AtomicReference;
 import java.util.logging.Level;
@@ -85,6 +86,8 @@ final class RegionalAccessBoundaryManager {
   private final AtomicReference<CooldownState> cooldownState =
       new AtomicReference<>(new CooldownState(0, INITIAL_COOLDOWN_MILLIS));
 
+  private final AtomicBoolean skipRAB = new AtomicBoolean(false);
+
   // Unbounded thread creation is discouraged in library code to avoid resource
   // exhaustion. A shared, bounded executor service ensures a hard limit (5)
   // on concurrent refresh tasks, while threadCount provides unique names
@@ -178,7 +181,7 @@ void triggerAsyncRefresh(
       final HttpTransportFactory transportFactory,
       final RegionalAccessBoundaryProvider provider,
       final AccessToken accessToken) {
-    if (isCooldownActive()) {
+    if (skipRAB.get() || isCooldownActive()) {
       return;
     }
 
@@ -196,6 +199,11 @@ void triggerAsyncRefresh(
           () -> {
             try {
               String url = provider.getRegionalAccessBoundaryUrl();
+              if (url == null) {
+                skipRAB.set(true);
+                future.set(null);
+                return;
+              }
               RegionalAccessBoundary newRAB =
                   RegionalAccessBoundary.refresh(
                       transportFactory, url, accessToken, clock, maxRetryElapsedTimeMillis);
@@ -279,6 +287,11 @@ long getCurrentCooldownMillis() {
     return cooldownState.get().durationMillis;
   }
 
+  @VisibleForTesting
+  boolean isSkipRAB() {
+    return skipRAB.get();
+  }
+
   private static class CooldownState {
     /** The time (in milliseconds from epoch) when the current cooldown period expires. */
     final long expiryTime;
diff --git a/google-auth-library-java/oauth2_http/javatests/com/google/auth/oauth2/ComputeEngineCredentialsTest.java b/google-auth-library-java/oauth2_http/javatests/com/google/auth/oauth2/ComputeEngineCredentialsTest.java
index 78bfd5ddaaa4..31eba072c2c5 100644
--- a/google-auth-library-java/oauth2_http/javatests/com/google/auth/oauth2/ComputeEngineCredentialsTest.java
+++ b/google-auth-library-java/oauth2_http/javatests/com/google/auth/oauth2/ComputeEngineCredentialsTest.java
@@ -1242,6 +1242,48 @@ void refresh_regionalAccessBoundarySuccess() throws IOException, InterruptedExce
         Arrays.asList(TestUtils.REGIONAL_ACCESS_BOUNDARY_ENCODED_LOCATION));
   }
 
+  @org.junit.jupiter.api.Test
+  void refresh_regionalAccessBoundaryNonEmail_skipsRABLookup()
+      throws IOException, InterruptedException {
+    String nonEmailAccount = "non-email-account-value";
+    MockMetadataServerTransportFactory transportFactory = new MockMetadataServerTransportFactory();
+    RegionalAccessBoundary regionalAccessBoundary =
+        new RegionalAccessBoundary(
+            TestUtils.REGIONAL_ACCESS_BOUNDARY_ENCODED_LOCATION,
+            TestUtils.REGIONAL_ACCESS_BOUNDARY_LOCATIONS,
+            null);
+    transportFactory.transport.setRegionalAccessBoundary(regionalAccessBoundary);
+    transportFactory.transport.setServiceAccountEmail(nonEmailAccount);
+
+    ComputeEngineCredentials credentials =
+        ComputeEngineCredentials.newBuilder().setHttpTransportFactory(transportFactory).build();
+
+    // Before any call, skipRAB flag should be false
+    assertFalse(credentials.regionalAccessBoundaryManager.isSkipRAB());
+
+    // First call: triggers lookup which determines non-email, returns null, and sets skipRAB to
+    // true
+    Map<String, List<String>> headers = credentials.getRequestMetadata();
+    assertNull(headers.get(X_ALLOWED_LOCATIONS_HEADER_KEY));
+
+    // Since the task is scheduled asynchronously on the shared executor, wait for it to complete
+    long deadline = System.currentTimeMillis() + 5000;
+    while (!credentials.regionalAccessBoundaryManager.isSkipRAB()
+        && System.currentTimeMillis() < deadline) {
+      Thread.sleep(50);
+    }
+
+    // Verify skipRAB flag has been set to true
+    assertTrue(credentials.regionalAccessBoundaryManager.isSkipRAB());
+
+    // Verify RAB is still null
+    assertNull(credentials.getRegionalAccessBoundary());
+
+    // Second call: should bypass triggerAsyncRefresh completely and remain null
+    headers = credentials.getRequestMetadata();
+    assertNull(headers.get(X_ALLOWED_LOCATIONS_HEADER_KEY));
+  }
+
   private void waitForRegionalAccessBoundary(GoogleCredentials credentials)
       throws InterruptedException {
     long deadline = System.currentTimeMillis() + 5000;