diff --git a/aom_util/aom_thread.h b/aom_util/aom_thread.h
index bda8b75..61f3449 100644
--- a/aom_util/aom_thread.h
+++ b/aom_util/aom_thread.h
@@ -37,16 +37,10 @@
 typedef HANDLE pthread_t;
 typedef CRITICAL_SECTION pthread_mutex_t;
 
-#if _WIN32_WINNT >= 0x0600  // Windows Vista / Server 2008 or greater
-#define USE_WINDOWS_CONDITION_VARIABLE
+#if _WIN32_WINNT < 0x0600
+#error Windows Vista / Server 2008 or greater is required.
+#endif
 typedef CONDITION_VARIABLE pthread_cond_t;
-#else
-typedef struct {
-  HANDLE waiting_sem_;
-  HANDLE received_sem_;
-  HANDLE signal_event_;
-} pthread_cond_t;
-#endif  // _WIN32_WINNT >= 0x600
 
 #ifndef WINAPI_FAMILY_PARTITION
 #define WINAPI_PARTITION_DESKTOP 1
@@ -64,11 +58,6 @@
 #define THREADFN unsigned int __stdcall
 #define THREAD_RETURN(val) (unsigned int)((DWORD_PTR)val)
 
-#if _WIN32_WINNT >= 0x0501  // Windows XP or greater
-#define WaitForSingleObject(obj, timeout) \
-  WaitForSingleObjectEx(obj, timeout, FALSE /*bAlertable*/)
-#endif
-
 static INLINE int pthread_create(pthread_t *const thread, const void *attr,
                                  unsigned int(__stdcall *start)(void *),
                                  void *arg) {
@@ -91,7 +80,8 @@
 
 static INLINE int pthread_join(pthread_t thread, void **value_ptr) {
   (void)value_ptr;
-  return (WaitForSingleObject(thread, INFINITE) != WAIT_OBJECT_0 ||
+  return (WaitForSingleObjectEx(thread, INFINITE, FALSE /*bAlertable*/) !=
+              WAIT_OBJECT_0 ||
           CloseHandle(thread) == 0);
 }
 
@@ -99,11 +89,7 @@
 static INLINE int pthread_mutex_init(pthread_mutex_t *const mutex,
                                      void *mutexattr) {
   (void)mutexattr;
-#if _WIN32_WINNT >= 0x0600  // Windows Vista / Server 2008 or greater
   InitializeCriticalSectionEx(mutex, 0 /*dwSpinCount*/, 0 /*Flags*/);
-#else
-  InitializeCriticalSection(mutex);
-#endif
   return 0;
 }
 
@@ -128,85 +114,31 @@
 
 // Condition
 static INLINE int pthread_cond_destroy(pthread_cond_t *const condition) {
-  int ok = 1;
-#ifdef USE_WINDOWS_CONDITION_VARIABLE
   (void)condition;
-#else
-  ok &= (CloseHandle(condition->waiting_sem_) != 0);
-  ok &= (CloseHandle(condition->received_sem_) != 0);
-  ok &= (CloseHandle(condition->signal_event_) != 0);
-#endif
-  return !ok;
+  return 0;
 }
 
 static INLINE int pthread_cond_init(pthread_cond_t *const condition,
                                     void *cond_attr) {
   (void)cond_attr;
-#ifdef USE_WINDOWS_CONDITION_VARIABLE
   InitializeConditionVariable(condition);
-#else
-  condition->waiting_sem_ = CreateSemaphore(NULL, 0, MAX_DECODE_THREADS, NULL);
-  condition->received_sem_ = CreateSemaphore(NULL, 0, MAX_DECODE_THREADS, NULL);
-  condition->signal_event_ = CreateEvent(NULL, FALSE, FALSE, NULL);
-  if (condition->waiting_sem_ == NULL || condition->received_sem_ == NULL ||
-      condition->signal_event_ == NULL) {
-    pthread_cond_destroy(condition);
-    return 1;
-  }
-#endif
   return 0;
 }
 
 static INLINE int pthread_cond_signal(pthread_cond_t *const condition) {
-  int ok = 1;
-#ifdef USE_WINDOWS_CONDITION_VARIABLE
   WakeConditionVariable(condition);
-#else
-  if (WaitForSingleObject(condition->waiting_sem_, 0) == WAIT_OBJECT_0) {
-    // a thread is waiting in pthread_cond_wait: allow it to be notified
-    ok = SetEvent(condition->signal_event_);
-    // wait until the event is consumed so the signaler cannot consume
-    // the event via its own pthread_cond_wait.
-    ok &= (WaitForSingleObject(condition->received_sem_, INFINITE) !=
-           WAIT_OBJECT_0);
-  }
-#endif
-  return !ok;
+  return 0;
 }
 
 static INLINE int pthread_cond_broadcast(pthread_cond_t *const condition) {
-  int ok = 1;
-#ifdef USE_WINDOWS_CONDITION_VARIABLE
   WakeAllConditionVariable(condition);
-#else
-  while (WaitForSingleObject(condition->waiting_sem_, 0) == WAIT_OBJECT_0) {
-    // a thread is waiting in pthread_cond_wait: allow it to be notified
-    ok &= SetEvent(condition->signal_event_);
-    // wait until the event is consumed so the signaler cannot consume
-    // the event via its own pthread_cond_wait.
-    ok &= (WaitForSingleObject(condition->received_sem_, INFINITE) !=
-           WAIT_OBJECT_0);
-  }
-#endif
-  return !ok;
+  return 0;
 }
 
 static INLINE int pthread_cond_wait(pthread_cond_t *const condition,
                                     pthread_mutex_t *const mutex) {
   int ok;
-#ifdef USE_WINDOWS_CONDITION_VARIABLE
   ok = SleepConditionVariableCS(condition, mutex, INFINITE);
-#else
-  // note that there is a consumer available so the signal isn't dropped in
-  // pthread_cond_signal
-  if (!ReleaseSemaphore(condition->waiting_sem_, 1, NULL)) return 1;
-  // now unlock the mutex so pthread_cond_signal may be issued
-  pthread_mutex_unlock(mutex);
-  ok = (WaitForSingleObject(condition->signal_event_, INFINITE) ==
-        WAIT_OBJECT_0);
-  ok &= ReleaseSemaphore(condition->received_sem_, 1, NULL);
-  pthread_mutex_lock(mutex);
-#endif
   return !ok;
 }
 #elif defined(__OS2__)