diff --git a/tests/Android.mk b/tests/Android.mk
index 890e203..59fe57d 100644
--- a/tests/Android.mk
+++ b/tests/Android.mk
@@ -86,6 +86,7 @@
     regex_test.cpp \
     sched_test.cpp \
     search_test.cpp \
+    semaphore_test.cpp \
     signal_test.cpp \
     stack_protector_test.cpp \
     stdatomic_test.cpp \
diff --git a/tests/semaphore_test.cpp b/tests/semaphore_test.cpp
new file mode 100644
index 0000000..e517f81
--- /dev/null
+++ b/tests/semaphore_test.cpp
@@ -0,0 +1,143 @@
+/*
+ * Copyright (C) 2014 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <semaphore.h>
+
+#include <errno.h>
+#include <gtest/gtest.h>
+#include <limits.h>
+#include <pthread.h>
+#include <time.h>
+#include <unistd.h>
+
+#include "private/bionic_constants.h"
+
+TEST(semaphore, sem_init) {
+  sem_t s;
+
+  // Perfectly fine initial values.
+  ASSERT_EQ(0, sem_init(&s, 0, 0));
+  ASSERT_EQ(0, sem_init(&s, 0, 1));
+  ASSERT_EQ(0, sem_init(&s, 0, 123));
+
+  // Too small an initial value.
+  errno = 0;
+  ASSERT_EQ(-1, sem_init(&s, 0, -1));
+  ASSERT_EQ(EINVAL, errno);
+
+  ASSERT_EQ(SEM_VALUE_MAX, sysconf(_SC_SEM_VALUE_MAX));
+
+  // The largest initial value.
+  ASSERT_EQ(0, sem_init(&s, 0, SEM_VALUE_MAX));
+
+  // Too large an initial value.
+  errno = 0;
+  ASSERT_EQ(-1, sem_init(&s, 0, SEM_VALUE_MAX + 1));
+  ASSERT_EQ(EINVAL, errno);
+
+  ASSERT_EQ(0, sem_destroy(&s));
+}
+
+TEST(semaphore, sem_trywait) {
+  sem_t s;
+  ASSERT_EQ(0, sem_init(&s, 0, 3));
+  ASSERT_EQ(0, sem_trywait(&s));
+  ASSERT_EQ(0, sem_trywait(&s));
+  ASSERT_EQ(0, sem_trywait(&s));
+  errno = 0;
+  ASSERT_EQ(-1, sem_trywait(&s));
+  ASSERT_EQ(EAGAIN, errno);
+  ASSERT_EQ(0, sem_destroy(&s));
+}
+
+static void SemWaitThreadTestFn(sem_t& sem) {
+  ASSERT_EQ(0, sem_wait(&sem));
+}
+
+static void* SemWaitThreadFn(void* arg) {
+  SemWaitThreadTestFn(*reinterpret_cast<sem_t*>(arg));
+  return nullptr;
+}
+
+TEST(semaphore, sem_wait__sem_post) {
+  sem_t s;
+  ASSERT_EQ(0, sem_init(&s, 0, 0));
+
+  pthread_t t1, t2, t3;
+  ASSERT_EQ(0, pthread_create(&t1, NULL, SemWaitThreadFn, &s));
+  ASSERT_EQ(0, pthread_create(&t2, NULL, SemWaitThreadFn, &s));
+  ASSERT_EQ(0, pthread_create(&t3, NULL, SemWaitThreadFn, &s));
+
+  ASSERT_EQ(0, sem_post(&s));
+  ASSERT_EQ(0, sem_post(&s));
+  ASSERT_EQ(0, sem_post(&s));
+
+  void* result;
+  ASSERT_EQ(0, pthread_join(t1, &result));
+  ASSERT_EQ(0, pthread_join(t2, &result));
+  ASSERT_EQ(0, pthread_join(t3, &result));
+}
+
+static inline void timespec_add_ms(timespec& ts, size_t ms) {
+  ts.tv_sec  += ms / 1000;
+  ts.tv_nsec += (ms % 1000) * 1000000;
+  if (ts.tv_nsec >= NS_PER_S) {
+    ts.tv_sec++;
+    ts.tv_nsec -= NS_PER_S;
+  }
+}
+
+TEST(semaphore, sem_timedwait) {
+  sem_t s;
+  ASSERT_EQ(0, sem_init(&s, 0, 0));
+
+  timespec ts;
+  ASSERT_EQ(0, clock_gettime(CLOCK_REALTIME, &ts));
+  timespec_add_ms(ts, 100);
+
+  errno = 0;
+  ASSERT_EQ(-1, sem_timedwait(&s, &ts));
+  ASSERT_EQ(ETIMEDOUT, errno);
+
+  // A negative timeout is an error.
+  errno = 0;
+  ts.tv_nsec = -1;
+  ASSERT_EQ(-1, sem_timedwait(&s, &ts));
+  ASSERT_EQ(EINVAL, errno);
+
+  ASSERT_EQ(0, sem_destroy(&s));
+}
+
+TEST(semaphore, sem_getvalue) {
+  sem_t s;
+  ASSERT_EQ(0, sem_init(&s, 0, 0));
+
+  int i;
+  ASSERT_EQ(0, sem_getvalue(&s, &i));
+  ASSERT_EQ(0, i);
+
+  ASSERT_EQ(0, sem_post(&s));
+  ASSERT_EQ(0, sem_getvalue(&s, &i));
+  ASSERT_EQ(1, i);
+
+  ASSERT_EQ(0, sem_post(&s));
+  ASSERT_EQ(0, sem_getvalue(&s, &i));
+  ASSERT_EQ(2, i);
+
+  ASSERT_EQ(0, sem_wait(&s));
+  ASSERT_EQ(0, sem_getvalue(&s, &i));
+  ASSERT_EQ(1, i);
+}
diff --git a/tests/time_test.cpp b/tests/time_test.cpp
index c9ead8d..c631b6a 100644
--- a/tests/time_test.cpp
+++ b/tests/time_test.cpp
@@ -26,6 +26,8 @@
 
 #include "ScopedSignalHandler.h"
 
+#include "private/bionic_constants.h"
+
 TEST(time, gmtime) {
   time_t t = 0;
   tm* broken_down = gmtime(&t);
@@ -395,7 +397,7 @@
   ts2.tv_nsec -= ts1.tv_nsec;
   if (ts2.tv_nsec < 0) {
     --ts2.tv_sec;
-    ts2.tv_nsec += 1000000000;
+    ts2.tv_nsec += NS_PER_S;
   }
 
   // Should be less than (a very generous, to try to avoid flakiness) 1000000ns.