diff --git a/meson.build b/meson.build
index 82e4a96f..76eaff20 100644
--- a/meson.build
+++ b/meson.build
@@ -22,6 +22,10 @@ datadir = get_option('datadir')
 sysconfdir = get_option('sysconfdir')
 prefix = get_option('prefix')
 
+if is_freebsd
+	add_project_arguments('-D_C11_SOURCE', language: 'c')
+endif
+
 swayidle_deps = []
 
 jsonc          = dependency('json-c', version: '>=0.13')