diff --git a/meson.build b/meson.build
index 86b8de77ad..0ff16b42d9 100644
--- a/meson.build
+++ b/meson.build
@@ -367,6 +367,7 @@ if not features['win32-threads']
     features += {'pthread-condattr-setclock':
                     cc.has_header_symbol('pthread.h',
                                          'pthread_condattr_setclock',
+                                         args: '-D_GNU_SOURCE',
                                          dependencies: pthreads)}
     dependencies += pthreads
 endif