diff --git a/crypto/crypto_test.cc b/crypto/crypto_test.cc
index caccba5..4543d5c 100644
--- a/crypto/crypto_test.cc
+++ b/crypto/crypto_test.cc
@@ -158,3 +158,12 @@
   BORINGSSL_integrity_test();
 }
 #endif
+
+OPENSSL_DEPRECATED static void DeprecatedFunction() {}
+
+OPENSSL_BEGIN_ALLOW_DEPRECATED
+TEST(CryptoTest, DeprecatedFunction) {
+  // This is deprecated, but should not trigger any warnings.
+  DeprecatedFunction();
+}
+OPENSSL_END_ALLOW_DEPRECATED
diff --git a/crypto/x509v3/v3_lib.c b/crypto/x509v3/v3_lib.c
index 52528ea..61cbeea 100644
--- a/crypto/x509v3/v3_lib.c
+++ b/crypto/x509v3/v3_lib.c
@@ -141,6 +141,7 @@
 }
 
 int X509V3_EXT_add_alias(int nid_to, int nid_from) {
+OPENSSL_BEGIN_ALLOW_DEPRECATED
   const X509V3_EXT_METHOD *ext;
   X509V3_EXT_METHOD *tmpext;
 
@@ -159,6 +160,7 @@
     return 0;
   }
   return 1;
+OPENSSL_END_ALLOW_DEPRECATED
 }
 
 // Legacy function: we don't need to add standard extensions any more because
diff --git a/include/openssl/base.h b/include/openssl/base.h
index fb1815f..80d18a7 100644
--- a/include/openssl/base.h
+++ b/include/openssl/base.h
@@ -221,6 +221,33 @@
 
 #endif  // defined(BORINGSSL_SHARED_LIBRARY)
 
+#if defined(_MSC_VER)
+
+// OPENSSL_DEPRECATED is used to mark a function as deprecated. Use
+// of any functions so marked in caller code will produce a warning.
+// OPENSSL_BEGIN_ALLOW_DEPRECATED and OPENSSL_END_ALLOW_DEPRECATED
+// can be used to suppress the warning in regions of caller code.
+#define OPENSSL_DEPRECATED __declspec(deprecated)
+#define OPENSSL_BEGIN_ALLOW_DEPRECATED \
+  __pragma(warning(push)) __pragma(warning(disable : 4996))
+#define OPENSSL_END_ALLOW_DEPRECATED __pragma(warning(pop))
+
+#elif defined(__GNUC__) || defined(__clang__)
+
+#define OPENSSL_DEPRECATED __attribute__((__deprecated__))
+#define OPENSSL_BEGIN_ALLOW_DEPRECATED \
+  _Pragma("GCC diagnostic push")       \
+      _Pragma("GCC diagnostic ignored \"-Wdeprecated-declarations\"")
+#define OPENSSL_END_ALLOW_DEPRECATED _Pragma("GCC diagnostic pop")
+
+#else
+
+#define OPENSSL_DEPRECATED
+#define OPENSSL_BEGIN_ALLOW_DEPRECATED
+#define OPENSSL_END_ALLOW_DEPRECATED
+
+#endif
+
 
 #if defined(__GNUC__) || defined(__clang__)
 // MinGW has two different printf implementations. Ensure the format macro
diff --git a/include/openssl/x509v3.h b/include/openssl/x509v3.h
index ee90f58..d9c862d 100644
--- a/include/openssl/x509v3.h
+++ b/include/openssl/x509v3.h
@@ -688,14 +688,15 @@
 // callers should simply handle the custom extension with the byte-based
 // |X509_EXTENSION| APIs directly. Registering |ext| with the library has little
 // practical value.
-OPENSSL_EXPORT int X509V3_EXT_add(X509V3_EXT_METHOD *ext);
+OPENSSL_EXPORT OPENSSL_DEPRECATED int X509V3_EXT_add(X509V3_EXT_METHOD *ext);
 
 // X509V3_EXT_add_alias registers a custom extension with NID |nid_to|. The
 // corresponding ASN.1 type is copied from |nid_from|. It returns one on success
 // and zero on error.
 //
 // WARNING: Do not use this function. See |X509V3_EXT_add|.
-OPENSSL_EXPORT int X509V3_EXT_add_alias(int nid_to, int nid_from);
+OPENSSL_EXPORT OPENSSL_DEPRECATED int X509V3_EXT_add_alias(int nid_to,
+                                                           int nid_from);
 
 OPENSSL_EXPORT const X509V3_EXT_METHOD *X509V3_EXT_get(
     const X509_EXTENSION *ext);