diff --git a/include/openssl/modes.h b/include/openssl/modes.h
index a04c6a5981ac40df528262e28b4a576886887377..d544f98d5585e9ab2e6b3ce68682607e7ba0c993 100644
--- a/include/openssl/modes.h
+++ b/include/openssl/modes.h
@@ -7,11 +7,14 @@
  * https://www.openssl.org/source/license.html
  */
 
-#include <stddef.h>
+#ifndef HEADER_MODES_H
+# define HEADER_MODES_H
 
-#ifdef  __cplusplus
+# include <stddef.h>
+
+# ifdef  __cplusplus
 extern "C" {
-#endif
+# endif
 typedef void (*block128_f) (const unsigned char in[16],
                             unsigned char out[16], const void *key);
 
@@ -166,7 +169,7 @@ size_t CRYPTO_128_unwrap_pad(void *key, const unsigned char *icv,
                              unsigned char *out, const unsigned char *in,
                              size_t inlen, block128_f block);
 
-#ifndef OPENSSL_NO_OCB
+# ifndef OPENSSL_NO_OCB
 typedef struct ocb128_context OCB128_CONTEXT;
 
 typedef void (*ocb128_f) (const unsigned char *in, unsigned char *out,
@@ -196,8 +199,10 @@ int CRYPTO_ocb128_finish(OCB128_CONTEXT *ctx, const unsigned char *tag,
                          size_t len);
 int CRYPTO_ocb128_tag(OCB128_CONTEXT *ctx, unsigned char *tag, size_t len);
 void CRYPTO_ocb128_cleanup(OCB128_CONTEXT *ctx);
-#endif                          /* OPENSSL_NO_OCB */
+# endif                          /* OPENSSL_NO_OCB */
 
-#ifdef  __cplusplus
+# ifdef  __cplusplus
 }
+# endif
+
 #endif