diff --git a/tests/thread_flags/main.c b/tests/thread_flags/main.c
index 153668073f..86ab454ab3 100644
--- a/tests/thread_flags/main.c
+++ b/tests/thread_flags/main.c
@@ -98,6 +98,14 @@ int main(void)
     uint32_t diff = xtimer_now_usec() - before;
     printf("main: timeout triggered. time passed: %"PRIu32"us\n", diff);
 
+    puts("main: setting 100ms timeout (using uint64)...");
+    uint64_t timeout64 = TIMEOUT;
+    before = xtimer_now_usec();
+    xtimer_set_timeout_flag64(&t, timeout64);
+    thread_flags_wait_any(THREAD_FLAG_TIMEOUT);
+    diff = xtimer_now_usec() - before;
+    printf("main: timeout triggered. time passed: %"PRIu32"us\n", diff);
+
     if (diff < (TIMEOUT + THRESHOLD)) {
         puts("SUCCESS");
         return 0;
diff --git a/tests/thread_flags/tests/01-run.py b/tests/thread_flags/tests/01-run.py
index 063a7dd55d..73e71eb017 100755
--- a/tests/thread_flags/tests/01-run.py
+++ b/tests/thread_flags/tests/01-run.py
@@ -24,6 +24,8 @@ def testfunc(child):
     child.expect_exact("thread(): received flags: 0x0008")
     child.expect_exact("main: setting 100ms timeout...")
     child.expect("main: timeout triggered. time passed: [0-9]{6}us")
+    child.expect_exact("main: setting 100ms timeout (using uint64)...")
+    child.expect("main: timeout triggered. time passed: [0-9]{6}us")
     child.expect("SUCCESS")