diff --git a/meson.build b/meson.build
index 6193357b186..23380319cc5 100644
--- a/meson.build
+++ b/meson.build
@@ -970,7 +970,7 @@ if cc.compiles('__uint128_t foo(void) { return 0; }',
 endif
 
 # TODO: this is very incomplete
-if ['linux', 'cygwin', 'gnu', 'freebsd', 'gnu/kfreebsd'].contains(host_machine.system())
+if ['linux', 'cygwin', 'gnu', 'freebsd', 'gnu/kfreebsd', 'haiku'].contains(host_machine.system())
   pre_args += '-D_GNU_SOURCE'
 elif host_machine.system() == 'sunos'
   pre_args += '-D__EXTENSIONS__'