diff --git a/tests/semaphore_test.cpp b/tests/semaphore_test.cpp
index e517f81..b65bfb8 100644
--- a/tests/semaphore_test.cpp
+++ b/tests/semaphore_test.cpp
@@ -117,6 +117,16 @@
   ts.tv_nsec = -1;
   ASSERT_EQ(-1, sem_timedwait(&s, &ts));
   ASSERT_EQ(EINVAL, errno);
+  errno = 0;
+  ts.tv_nsec = NS_PER_S;
+  ASSERT_EQ(-1, sem_timedwait(&s, &ts));
+  ASSERT_EQ(EINVAL, errno);
+
+  errno = 0;
+  ts.tv_nsec = NS_PER_S - 1;
+  ts.tv_sec = -1;
+  ASSERT_EQ(-1, sem_timedwait(&s, &ts));
+  ASSERT_EQ(ETIMEDOUT, errno);
 
   ASSERT_EQ(0, sem_destroy(&s));
 }