diff --git a/expat/ConfigureChecks.cmake b/expat/ConfigureChecks.cmake
index 10e3bb19..c06b2f27 100644
--- a/expat/ConfigureChecks.cmake
+++ b/expat/ConfigureChecks.cmake
@@ -60,6 +60,7 @@ if(NOT HAVE_OFF_T)
 endif()
 
 check_c_source_compiles("
+        #define _GNU_SOURCE
         #include <stdlib.h>  /* for NULL */
         #include <unistd.h>  /* for syscall */
         #include <sys/syscall.h>  /* for SYS_getrandom */
diff --git a/expat/configure.ac b/expat/configure.ac
index 5baf0a62..9d28d79a 100644
--- a/expat/configure.ac
+++ b/expat/configure.ac
@@ -274,6 +274,7 @@ AS_HELP_STRING([--without-sys-getrandom],
 AS_IF([test "x$with_sys_getrandom" != xno],
   [AC_MSG_CHECKING([for syscall SYS_getrandom (Linux 3.17+)])
    AC_LINK_IFELSE([AC_LANG_SOURCE([
+       #define _GNU_SOURCE
        #include <stdlib.h>  /* for NULL */
        #include <unistd.h>  /* for syscall */
        #include <sys/syscall.h>  /* for SYS_getrandom */