diff --git a/include/__threading_support b/include/__threading_support
index a672a9f80..c8ce331cd 100644
--- a/include/__threading_support
+++ b/include/__threading_support
@@ -102,7 +102,7 @@ _LIBCPP_THREAD_ABI_VISIBILITY
 int __libcpp_recursive_mutex_lock(__libcpp_recursive_mutex_t *__m);
 
 _LIBCPP_THREAD_ABI_VISIBILITY
-int __libcpp_recursive_mutex_trylock(__libcpp_recursive_mutex_t *__m);
+bool __libcpp_recursive_mutex_trylock(__libcpp_recursive_mutex_t *__m);
 
 _LIBCPP_THREAD_ABI_VISIBILITY
 int __libcpp_recursive_mutex_unlock(__libcpp_recursive_mutex_t *__m);
@@ -114,7 +114,7 @@ _LIBCPP_THREAD_ABI_VISIBILITY
 int __libcpp_mutex_lock(__libcpp_mutex_t *__m);
 
 _LIBCPP_THREAD_ABI_VISIBILITY
-int __libcpp_mutex_trylock(__libcpp_mutex_t *__m);
+bool __libcpp_mutex_trylock(__libcpp_mutex_t *__m);
 
 _LIBCPP_THREAD_ABI_VISIBILITY
 int __libcpp_mutex_unlock(__libcpp_mutex_t *__m);
@@ -221,9 +221,9 @@ int __libcpp_recursive_mutex_lock(__libcpp_recursive_mutex_t *__m)
   return pthread_mutex_lock(__m);
 }
 
-int __libcpp_recursive_mutex_trylock(__libcpp_recursive_mutex_t *__m)
+bool __libcpp_recursive_mutex_trylock(__libcpp_recursive_mutex_t *__m)
 {
-  return pthread_mutex_trylock(__m);
+  return pthread_mutex_trylock(__m) == 0;
 }
 
 int __libcpp_recursive_mutex_unlock(__libcpp_mutex_t *__m)
@@ -241,9 +241,9 @@ int __libcpp_mutex_lock(__libcpp_mutex_t *__m)
   return pthread_mutex_lock(__m);
 }
 
-int __libcpp_mutex_trylock(__libcpp_mutex_t *__m)
+bool __libcpp_mutex_trylock(__libcpp_mutex_t *__m)
 {
-  return pthread_mutex_trylock(__m);
+  return pthread_mutex_trylock(__m) == 0;
 }
 
 int __libcpp_mutex_unlock(__libcpp_mutex_t *__m)
@@ -371,10 +371,9 @@ int __libcpp_recursive_mutex_lock(__libcpp_recursive_mutex_t *__m)
   return 0;
 }
 
-int __libcpp_recursive_mutex_trylock(__libcpp_recursive_mutex_t *__m)
+bool __libcpp_recursive_mutex_trylock(__libcpp_recursive_mutex_t *__m)
 {
-  TryEnterCriticalSection(__m);
-  return 0;
+  return TryEnterCriticalSection(__m) != 0;
 }
 
 int __libcpp_recursive_mutex_unlock(__libcpp_recursive_mutex_t *__m)
@@ -395,10 +394,9 @@ int __libcpp_mutex_lock(__libcpp_mutex_t *__m)
   return 0;
 }
 
-int __libcpp_mutex_trylock(__libcpp_mutex_t *__m)
+bool __libcpp_mutex_trylock(__libcpp_mutex_t *__m)
 {
-  TryAcquireSRWLockExclusive(__m);
-  return 0;
+  return TryAcquireSRWLockExclusive(__m) != 0;
 }
 
 int __libcpp_mutex_unlock(__libcpp_mutex_t *__m)
diff --git a/src/mutex.cpp b/src/mutex.cpp
index 9397ae73c..338b79f2f 100644
--- a/src/mutex.cpp
+++ b/src/mutex.cpp
@@ -37,7 +37,7 @@ mutex::lock()
 bool
 mutex::try_lock() _NOEXCEPT
 {
-    return __libcpp_mutex_trylock(&__m_) == 0;
+    return __libcpp_mutex_trylock(&__m_);
 }
 
 void
@@ -83,7 +83,7 @@ recursive_mutex::unlock() _NOEXCEPT
 bool
 recursive_mutex::try_lock() _NOEXCEPT
 {
-    return __libcpp_recursive_mutex_trylock(&__m_) == 0;
+    return __libcpp_recursive_mutex_trylock(&__m_);
 }
 
 // timed_mutex
diff --git a/test/libcxx/test/config.py b/test/libcxx/test/config.py
index 49347dfe5..2478bacb2 100644
--- a/test/libcxx/test/config.py
+++ b/test/libcxx/test/config.py
@@ -382,6 +382,9 @@ class Configuration(object):
         if '__cpp_structured_bindings' not in macros:
             self.config.available_features.add('libcpp-no-structured-bindings')
 
+        if self.is_windows:
+            self.config.available_features.add('windows')
+
     def configure_compile_flags(self):
         no_default_flags = self.get_lit_bool('no_default_flags', False)
         if not no_default_flags: