diff --git a/meson.build b/meson.build
index 9911afb0e7..9fc45abc02 100644
--- a/meson.build
+++ b/meson.build
@@ -455,7 +455,8 @@ endforeach
 
 foreach ident : [
         ['memfd_create',      '''#include <sys/mman.h>'''],
-        ['gettid',            '''#include <sys/types.h>'''],
+        ['gettid',            '''#include <sys/types.h>
+                                 #include <unistd.h>'''],
         ['pivot_root',        '''#include <stdlib.h>
                                  #include <unistd.h>'''],     # no known header declares pivot_root
         ['name_to_handle_at', '''#include <sys/types.h>