diff --git a/meson.build b/meson.build
index 788681bc..341d567f 100644
--- a/meson.build
+++ b/meson.build
@@ -360,7 +360,8 @@ conf.set10('HAVE_DECL_VASPRINTF',
                                 prefix: '#define _GNU_SOURCE'))
 
 conf.set10('HAVE_DECL_REALLOCARRAY',
-           cc.has_header_symbol('stdlib.h', 'reallocarray'))
+           cc.has_header_symbol('stdlib.h', 'reallocarray',
+                               prefix: '#define _GNU_SOURCE'))
 
 # --------------------------------------------------------------------
 # libffi