diff --git a/lib/core/private-lib-core.h b/lib/core/private-lib-core.h
index 2b5b959f8..283c1ef30 100644
--- a/lib/core/private-lib-core.h
+++ b/lib/core/private-lib-core.h
@@ -29,7 +29,7 @@
 #include "lws_config_private.h"
 
 #if defined(LWS_WITH_CGI) && defined(LWS_HAVE_VFORK) && \
-    !defined(NO_GNU_SOURCE_THIS_TIME)
+    !defined(NO_GNU_SOURCE_THIS_TIME) && !defined(_GNU_SOURCE)
  #define  _GNU_SOURCE
 #endif
 
diff --git a/lib/misc/dir.c b/lib/misc/dir.c
index 8e712fec8..7a296a9f9 100644
--- a/lib/misc/dir.c
+++ b/lib/misc/dir.c
@@ -22,8 +22,12 @@
  * IN THE SOFTWARE.
  */
 
+#if !defined(NO_GNU_SOURCE_THIS_TIME)
 #define NO_GNU_SOURCE_THIS_TIME
+#endif
+#if !defined(_DARWIN_C_SOURCE)
 #define _DARWIN_C_SOURCE
+#endif
 
 #include <libwebsockets.h>
 #include "private-lib-core.h"
diff --git a/lib/misc/diskcache.c b/lib/misc/diskcache.c
index d2d364204..a90070ac5 100644
--- a/lib/misc/diskcache.c
+++ b/lib/misc/diskcache.c
@@ -22,7 +22,9 @@
  * IN THE SOFTWARE.
  */
 
+#if !defined(_GNU_SOURCE)
 #define _GNU_SOURCE
+#endif
 #include <pthread.h>
 
 #include "private-lib-core.h"
diff --git a/lib/misc/threadpool/threadpool.c b/lib/misc/threadpool/threadpool.c
index 7ac27e369..7415d6065 100644
--- a/lib/misc/threadpool/threadpool.c
+++ b/lib/misc/threadpool/threadpool.c
@@ -22,7 +22,10 @@
  * IN THE SOFTWARE.
  */
 
+#if !defined(_GNU_SOURCE)
 #define _GNU_SOURCE
+#endif
+
 #include <pthread.h>
 
 #include "private-lib-core.h"
diff --git a/lib/plat/unix/unix-caps.c b/lib/plat/unix/unix-caps.c
index 3647071e2..d3177a0d2 100644
--- a/lib/plat/unix/unix-caps.c
+++ b/lib/plat/unix/unix-caps.c
@@ -22,7 +22,9 @@
  * IN THE SOFTWARE.
  */
 
+#if !defined(_GNU_SOURCE)
 #define _GNU_SOURCE
+#endif
 #include "private-lib-core.h"
 
 #include <pwd.h>
diff --git a/lib/plat/unix/unix-fds.c b/lib/plat/unix/unix-fds.c
index dd7369f64..b1d3f1c07 100644
--- a/lib/plat/unix/unix-fds.c
+++ b/lib/plat/unix/unix-fds.c
@@ -22,7 +22,9 @@
  * IN THE SOFTWARE.
  */
 
+#if !defined(_GNU_SOURCE)
 #define _GNU_SOURCE
+#endif
 #include "private-lib-core.h"
 
 struct lws *
diff --git a/lib/plat/unix/unix-file.c b/lib/plat/unix/unix-file.c
index dbcf41cd1..1a8bd41ce 100644
--- a/lib/plat/unix/unix-file.c
+++ b/lib/plat/unix/unix-file.c
@@ -22,7 +22,9 @@
  * IN THE SOFTWARE.
  */
 
+#if !defined(_GNU_SOURCE)
 #define _GNU_SOURCE
+#endif
 #include "private-lib-core.h"
 
 #include <pwd.h>
diff --git a/lib/plat/unix/unix-init.c b/lib/plat/unix/unix-init.c
index 1ae066b40..24490bbc0 100644
--- a/lib/plat/unix/unix-init.c
+++ b/lib/plat/unix/unix-init.c
@@ -22,7 +22,9 @@
  * IN THE SOFTWARE.
  */
 
+#if !defined(_GNU_SOURCE)
 #define _GNU_SOURCE
+#endif
 #include "private-lib-core.h"
 
 #include <pwd.h>
diff --git a/lib/plat/unix/unix-misc.c b/lib/plat/unix/unix-misc.c
index 07ca41982..05b4d7ee1 100644
--- a/lib/plat/unix/unix-misc.c
+++ b/lib/plat/unix/unix-misc.c
@@ -22,7 +22,9 @@
  * IN THE SOFTWARE.
  */
 
+#if !defined(_GNU_SOURCE)
 #define _GNU_SOURCE
+#endif
 #include "private-lib-core.h"
 
 lws_usec_t
diff --git a/lib/plat/unix/unix-pipe.c b/lib/plat/unix/unix-pipe.c
index dc684a725..4786170d3 100644
--- a/lib/plat/unix/unix-pipe.c
+++ b/lib/plat/unix/unix-pipe.c
@@ -22,7 +22,9 @@
  * IN THE SOFTWARE.
  */
 
+#if !defined(_GNU_SOURCE)
 #define _GNU_SOURCE
+#endif
 #include "private-lib-core.h"
 
 
diff --git a/lib/plat/unix/unix-plugins.c b/lib/plat/unix/unix-plugins.c
index b34cce53c..259a53d63 100644
--- a/lib/plat/unix/unix-plugins.c
+++ b/lib/plat/unix/unix-plugins.c
@@ -22,7 +22,9 @@
  * IN THE SOFTWARE.
  */
 
+#if !defined(_GNU_SOURCE)
 #define _GNU_SOURCE
+#endif
 #include "private-lib-core.h"
 
 #include <pwd.h>
diff --git a/lib/plat/unix/unix-service.c b/lib/plat/unix/unix-service.c
index 304f14814..c1b993401 100644
--- a/lib/plat/unix/unix-service.c
+++ b/lib/plat/unix/unix-service.c
@@ -22,7 +22,9 @@
  * IN THE SOFTWARE.
  */
 
+#if !defined(_GNU_SOURCE)
 #define _GNU_SOURCE
+#endif
 #include "private-lib-core.h"
 
 int
diff --git a/lib/plat/unix/unix-sockets.c b/lib/plat/unix/unix-sockets.c
index 7c054c898..275d168ab 100644
--- a/lib/plat/unix/unix-sockets.c
+++ b/lib/plat/unix/unix-sockets.c
@@ -22,7 +22,9 @@
  * IN THE SOFTWARE.
  */
 
+#if !defined(_GNU_SOURCE)
 #define _GNU_SOURCE
+#endif
 #include "private-lib-core.h"
 
 #include <sys/ioctl.h>
diff --git a/lib/roles/cgi/cgi-server.c b/lib/roles/cgi/cgi-server.c
index eac732245..b34a33dad 100644
--- a/lib/roles/cgi/cgi-server.c
+++ b/lib/roles/cgi/cgi-server.c
@@ -22,7 +22,9 @@
  * IN THE SOFTWARE.
  */
 
-#define  _GNU_SOURCE
+#if !defined(_GNU_SOURCE)
+#define _GNU_SOURCE
+#endif
 
 #include "private-lib-core.h"