diff --git a/crypto/bio/bio_test.c b/crypto/bio/bio_test.c
index 4b0ab08f..fd88b55f 100644
--- a/crypto/bio/bio_test.c
+++ b/crypto/bio/bio_test.c
@@ -12,7 +12,7 @@
  * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
  * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
 
-#define _BSD_SOURCE
+#define _POSIX_C_SOURCE 201410L
 
 #include <openssl/base.h>
 
diff --git a/crypto/bio/printf.c b/crypto/bio/printf.c
index e1ae5b42..3638915b 100644
--- a/crypto/bio/printf.c
+++ b/crypto/bio/printf.c
@@ -54,8 +54,8 @@
  * copied and put under another distribution licence
  * [including the GNU Public Licence.] */
 
-#if !defined(_BSD_SOURCE)
-#define _BSD_SOURCE  /* for snprintf, vprintf etc */
+#if !defined(_POSIX_C_SOURCE)
+#define _POSIX_C_SOURCE 201410L  /* for snprintf, vprintf etc */
 #endif
 
 #include <openssl/bio.h>
diff --git a/crypto/lhash/lhash_test.c b/crypto/lhash/lhash_test.c
index eb40cab2..e47e96fa 100644
--- a/crypto/lhash/lhash_test.c
+++ b/crypto/lhash/lhash_test.c
@@ -12,7 +12,7 @@
  * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
  * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
 
-#define _BSD_SOURCE
+#define _POSIX_C_SOURCE 201410L
 
 #include <openssl/crypto.h>
 #include <openssl/lhash.h>
diff --git a/crypto/mem.c b/crypto/mem.c
index 1eb97c9f..b16b3104 100644
--- a/crypto/mem.c
+++ b/crypto/mem.c
@@ -53,9 +53,7 @@
  * copied and put under another distribution licence
  * [including the GNU Public Licence.] */
 
-#if !defined(_BSD_SOURCE)
-#define _BSD_SOURCE /* needed for strdup, snprintf, vprintf etc */
-#endif
+#define _POSIX_C_SOURCE 201410L  /* needed for strdup, snprintf, vprintf etc */
 
 #include <openssl/mem.h>
 
@@ -66,6 +64,8 @@
 
 #if defined(OPENSSL_WINDOWS)
 #include <Windows.h>
+#else
+#include <strings.h>
 #endif
 
 
diff --git a/crypto/time_support.c b/crypto/time_support.c
index 5b300b37..4537e82b 100644
--- a/crypto/time_support.c
+++ b/crypto/time_support.c
@@ -55,9 +55,7 @@
  * (eay@cryptsoft.com).  This product includes software written by Tim
  * Hudson (tjh@cryptsoft.com). */
 
-#if !defined(_BSD_SOURCE)
-#define _BSD_SOURCE /* for gmtime_r */
-#endif
+#define _POSIX_C_SOURCE 201410L  /* for gmtime_r */
 
 #include <openssl/time_support.h>