diff --git a/src/cpp/client/secure_credentials.h b/src/cpp/client/secure_credentials.h
index eb6823884401aa73e011d681443e15af0ffb355b..77d575813eae2968b6139862a385d0aaf1d0b71d 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 @@ class SecureCredentials GRPC_FINAL : public Credentials {
 
 }  // 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 fa49d30743f82c0483d9ac93fcc464aa74357348..b9803f107e5d587774809d2b694ca5ed4f5b4402 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 @@ class SecureServerCredentials GRPC_FINAL : public ServerCredentials {
 
 }  // namespace grpc
 
+#endif  // GRPC_INTERNAL_CPP_SERVER_SECURE_SERVER_CREDENTIALS_H