Guard headers tool.
diff --git a/test/core/end2end/end2end_tests.h b/test/core/end2end/end2end_tests.h
index 8f2cd0f..b6d9325 100644
--- a/test/core/end2end/end2end_tests.h
+++ b/test/core/end2end/end2end_tests.h
@@ -31,8 +31,8 @@
  *
  */
 
-#ifndef __GRPC_TEST_END2END_END2END_TESTS_H__
-#define __GRPC_TEST_END2END_END2END_TESTS_H__
+#ifndef GRPC_TEST_CORE_END2END_END2END_TESTS_H
+#define GRPC_TEST_CORE_END2END_END2END_TESTS_H
 
 #include <grpc/grpc.h>
 
@@ -63,4 +63,4 @@
 
 void grpc_end2end_tests(grpc_end2end_test_config config);
 
-#endif /* __GRPC_TEST_END2END_END2END_TESTS_H__ */
+#endif  /* GRPC_TEST_CORE_END2END_END2END_TESTS_H */