Addressing comments.
diff --git a/src/cpp/client/secure_credentials.h b/src/cpp/client/secure_credentials.h
index eb68238..77d5758 100644
--- a/src/cpp/client/secure_credentials.h
+++ b/src/cpp/client/secure_credentials.h
@@ -31,6 +31,9 @@
  *
  */
 
+#ifndef GRPC_INTERNAL_CPP_CLIENT_SECURE_CREDENTIALS_H
+#define GRPC_INTERNAL_CPP_CLIENT_SECURE_CREDENTIALS_H
+
 #include <grpc/grpc_security.h>
 
 #include <grpc++/config.h>
@@ -54,4 +57,5 @@
 
 }  // namespace grpc
 
+#endif  // GRPC_INTERNAL_CPP_CLIENT_SECURE_CREDENTIALS_H
 
diff --git a/src/cpp/server/secure_server_credentials.h b/src/cpp/server/secure_server_credentials.h
index fa49d30..b9803f1 100644
--- a/src/cpp/server/secure_server_credentials.h
+++ b/src/cpp/server/secure_server_credentials.h
@@ -31,6 +31,9 @@
  *
  */
 
+#ifndef GRPC_INTERNAL_CPP_SERVER_SECURE_SERVER_CREDENTIALS_H
+#define GRPC_INTERNAL_CPP_SERVER_SECURE_SERVER_CREDENTIALS_H
+
 #include <grpc/grpc_security.h>
 
 #include <grpc++/server_credentials.h>
@@ -54,3 +57,4 @@
 
 }  // namespace grpc
 
+#endif  // GRPC_INTERNAL_CPP_SERVER_SECURE_SERVER_CREDENTIALS_H