diff --git a/src/Makefile b/src/Makefile
index a6f380b6f..291508edc 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -307,6 +307,7 @@ endif
 #  -Wno-missing-braces      ignore invalid warning (GCC bug 53119)
 #  -Wno-unused-value        ignore unused return values of some functions (i.e. fread())
 #  -D_DEFAULT_SOURCE        use with -std=c99 on Linux and PLATFORM_WEB, required for timespec
+#  -D_GNU_SOURCE            access to lots of nonstandard GNU/Linux extension functions
 #  -Werror=pointer-arith    catch unportable code that does direct arithmetic on void pointers
 #  -fno-strict-aliasing     jar_xm.h does shady stuff (breaks strict aliasing)
 CFLAGS = -Wall -D_GNU_SOURCE -D$(PLATFORM) -D$(GRAPHICS) -Wno-missing-braces -Werror=pointer-arith -fno-strict-aliasing $(CUSTOM_CFLAGS)
diff --git a/src/external/glfw/src/posix_poll.c b/src/external/glfw/src/posix_poll.c
index d309292e1..676a8a510 100644
--- a/src/external/glfw/src/posix_poll.c
+++ b/src/external/glfw/src/posix_poll.c
@@ -29,7 +29,6 @@
 #define _GNU_SOURCE
 
 #include "internal.h"
-#include "posix_poll.h"     // @raysan5: Required for poll(), ppoll()
 
 #include <signal.h>
 #include <time.h>
diff --git a/src/external/glfw/src/posix_poll.h b/src/external/glfw/src/posix_poll.h
index 860f108da..1effd1cd3 100644
--- a/src/external/glfw/src/posix_poll.h
+++ b/src/external/glfw/src/posix_poll.h
@@ -26,7 +26,6 @@
 // It is fine to use C99 in this file because it will not be built with VS
 //========================================================================
 
-#define _GNU_SOURCE     // @raysan5: Required for ppoll()
 #include <poll.h>
 
 GLFWbool _glfwPollPOSIX(struct pollfd* fds, nfds_t count, double* timeout);