diff --git a/js/src/threading/ConditionVariable.h b/js/src/threading/ConditionVariable.h
index 35eeaeeb08b8..976cd1937a9e 100644
--- a/js/src/threading/ConditionVariable.h
+++ b/js/src/threading/ConditionVariable.h
@@ -21,21 +21,19 @@
 
 namespace js {
 
-template <typename T> using UniqueLock = LockGuard<T>;
-
 enum class CVStatus {
   NoTimeout,
   Timeout
 };
 
-// A poly-fill for std::condition_variable.
-class ConditionVariable
-{
+namespace detail {
+
+class ConditionVariableImpl {
 public:
   struct PlatformData;
 
-  ConditionVariable();
-  ~ConditionVariable();
+  ConditionVariableImpl();
+  ~ConditionVariableImpl();
 
   // Wake one thread that is waiting on this condition.
   void notify_one();
@@ -45,7 +43,55 @@ public:
 
   // Block the current thread of execution until this condition variable is
   // woken from another thread via notify_one or notify_all.
-  void wait(UniqueLock<Mutex>& lock);
+  void wait(Mutex& lock);
+
+  CVStatus wait_for(Mutex& lock,
+                    const mozilla::TimeDuration& rel_time);
+
+private:
+  ConditionVariableImpl(const ConditionVariableImpl&) = delete;
+  ConditionVariableImpl& operator=(const ConditionVariableImpl&) = delete;
+
+  PlatformData* platformData();
+
+#ifndef XP_WIN
+  void* platformData_[sizeof(pthread_cond_t) / sizeof(void*)];
+  static_assert(sizeof(pthread_cond_t) / sizeof(void*) != 0 &&
+                sizeof(pthread_cond_t) % sizeof(void*) == 0,
+                "pthread_cond_t must have pointer alignment");
+#else
+  void* platformData_[4];
+#endif
+};
+
+} // namespace detail
+
+template <typename T> using UniqueLock = LockGuard<T>;
+
+// A poly-fill for std::condition_variable.
+class ConditionVariable
+{
+public:
+  struct PlatformData;
+
+  ConditionVariable() = default;
+  ~ConditionVariable() = default;
+
+  // Wake one thread that is waiting on this condition.
+  void notify_one() {
+    impl_.notify_one();
+  }
+
+  // Wake all threads that are waiting on this condition.
+  void notify_all() {
+    impl_.notify_all();
+  }
+
+  // Block the current thread of execution until this condition variable is
+  // woken from another thread via notify_one or notify_all.
+  void wait(UniqueLock<Mutex>& lock) {
+    impl_.wait(lock.lock);
+  }
 
   // As with |wait|, block the current thread of execution until woken from
   // another thread. This method will resume waiting once woken until the given
@@ -88,7 +134,9 @@ public:
   // has a minimum granularity of the system's scheduling interval, and may
   // encounter substantially longer delays, depending on system load.
   CVStatus wait_for(UniqueLock<Mutex>& lock,
-                    const mozilla::TimeDuration& rel_time);
+                    const mozilla::TimeDuration& rel_time) {
+    return impl_.wait_for(lock.lock, rel_time);
+  }
 
   // As with |wait_for|, block the current thread of execution until woken from
   // another thread or the given time duration has elapsed. This method will
@@ -106,16 +154,7 @@ private:
   ConditionVariable(const ConditionVariable&) = delete;
   ConditionVariable& operator=(const ConditionVariable&) = delete;
 
-  PlatformData* platformData();
-
-#ifndef XP_WIN
-  void* platformData_[sizeof(pthread_cond_t) / sizeof(void*)];
-  static_assert(sizeof(pthread_cond_t) / sizeof(void*) != 0 &&
-                sizeof(pthread_cond_t) % sizeof(void*) == 0,
-                "pthread_cond_t must have pointer alignment");
-#else
-  void* platformData_[4];
-#endif
+  detail::ConditionVariableImpl impl_;
 };
 
 } // namespace js
diff --git a/js/src/threading/Mutex.h b/js/src/threading/Mutex.h
index 2b300842f126..f6b0ea0a3b63 100644
--- a/js/src/threading/Mutex.h
+++ b/js/src/threading/Mutex.h
@@ -14,10 +14,10 @@
 
 namespace js {
 
-class ConditionVariable;
-
 namespace detail {
 
+class ConditionVariableImpl;
+
 class MutexImpl
 {
 public:
@@ -57,7 +57,7 @@ private:
   void* platformData_[64 / sizeof(void*)];
 #endif
 
-  friend class js::ConditionVariable;
+  friend class js::detail::ConditionVariableImpl;
 };
 
 } // namespace detail
diff --git a/js/src/threading/posix/ConditionVariable.cpp b/js/src/threading/posix/ConditionVariable.cpp
index cd0a35b46e04..2dd69739ba03 100644
--- a/js/src/threading/posix/ConditionVariable.cpp
+++ b/js/src/threading/posix/ConditionVariable.cpp
@@ -61,12 +61,12 @@ moz_timespecadd(struct timespec* lhs, struct timespec* rhs, struct timespec* res
 }
 #endif
 
-struct js::ConditionVariable::PlatformData
+struct js::detail::ConditionVariableImpl::PlatformData
 {
   pthread_cond_t ptCond;
 };
 
-js::ConditionVariable::ConditionVariable()
+js::detail::ConditionVariableImpl::ConditionVariableImpl()
 {
   pthread_cond_t* ptCond = &platformData()->ptCond;
 
@@ -89,39 +89,39 @@ js::ConditionVariable::ConditionVariable()
 #endif
 }
 
-js::ConditionVariable::~ConditionVariable()
+js::detail::ConditionVariableImpl::~ConditionVariableImpl()
 {
   int r = pthread_cond_destroy(&platformData()->ptCond);
   MOZ_RELEASE_ASSERT(r == 0);
 }
 
 void
-js::ConditionVariable::notify_one()
+js::detail::ConditionVariableImpl::notify_one()
 {
   int r = pthread_cond_signal(&platformData()->ptCond);
   MOZ_RELEASE_ASSERT(r == 0);
 }
 
 void
-js::ConditionVariable::notify_all()
+js::detail::ConditionVariableImpl::notify_all()
 {
   int r = pthread_cond_broadcast(&platformData()->ptCond);
   MOZ_RELEASE_ASSERT(r == 0);
 }
 
 void
-js::ConditionVariable::wait(UniqueLock<Mutex>& lock)
+js::detail::ConditionVariableImpl::wait(Mutex& lock)
 {
   pthread_cond_t* ptCond = &platformData()->ptCond;
-  pthread_mutex_t* ptMutex = &lock.lock.platformData()->ptMutex;
+  pthread_mutex_t* ptMutex = &lock.platformData()->ptMutex;
 
   int r = pthread_cond_wait(ptCond, ptMutex);
   MOZ_RELEASE_ASSERT(r == 0);
 }
 
 js::CVStatus
-js::ConditionVariable::wait_for(UniqueLock<Mutex>& lock,
-                                const TimeDuration& a_rel_time)
+js::detail::ConditionVariableImpl::wait_for(Mutex& lock,
+                                              const TimeDuration& a_rel_time)
 {
   if (a_rel_time == TimeDuration::Forever()) {
     wait(lock);
@@ -129,7 +129,7 @@ js::ConditionVariable::wait_for(UniqueLock<Mutex>& lock,
   }
 
   pthread_cond_t* ptCond = &platformData()->ptCond;
-  pthread_mutex_t* ptMutex = &lock.lock.platformData()->ptMutex;
+  pthread_mutex_t* ptMutex = &lock.platformData()->ptMutex;
   int r;
 
   // Clamp to 0, as time_t is unsigned.
@@ -164,8 +164,8 @@ js::ConditionVariable::wait_for(UniqueLock<Mutex>& lock,
   return CVStatus::Timeout;
 }
 
-js::ConditionVariable::PlatformData*
-js::ConditionVariable::platformData()
+js::detail::ConditionVariableImpl::PlatformData*
+js::detail::ConditionVariableImpl::platformData()
 {
   static_assert(sizeof platformData_ >= sizeof(PlatformData),
                 "platformData_ is too small");
diff --git a/js/src/threading/windows/ConditionVariable.cpp b/js/src/threading/windows/ConditionVariable.cpp
index 8c900751414d..8c27400891d9 100644
--- a/js/src/threading/windows/ConditionVariable.cpp
+++ b/js/src/threading/windows/ConditionVariable.cpp
@@ -29,41 +29,41 @@
 #endif
 
 // Wrapper for native condition variable APIs.
-struct js::ConditionVariable::PlatformData
+struct js::ConditionVariableImpl::PlatformData
 {
   CONDITION_VARIABLE cv_;
 };
 
-js::ConditionVariable::ConditionVariable()
+js::detail::ConditionVariableImpl::ConditionVariableImpl()
 {
   InitializeConditionVariable(&platformData()->cv_);
 }
 
 void
-js::ConditionVariable::notify_one()
+js::detail::ConditionVariableImpl::notify_one()
 {
   WakeConditionVariable(&platformData()->cv_);
 }
 
 void
-js::ConditionVariable::notify_all()
+js::detail::ConditionVariableImpl::notify_all()
 {
   WakeAllConditionVariable(&platformData()->cv_);
 }
 
 void
-js::ConditionVariable::wait(UniqueLock<Mutex>& lock)
+js::detail::ConditionVariableImpl::wait(Mutex& lock)
 {
-  CRITICAL_SECTION* cs = &lock.lock.platformData()->criticalSection;
+  CRITICAL_SECTION* cs = &lock.platformData()->criticalSection;
   bool r = SleepConditionVariableCS(&platformData()->cv_, cs, INFINITE);
   MOZ_RELEASE_ASSERT(r);
 }
 
 js::CVStatus
-js::ConditionVariable::wait_for(UniqueLock<Mutex>& lock,
-                                const mozilla::TimeDuration& rel_time)
+js::detail::ConditionVariableImpl::wait_for(Mutex& lock,
+                                              const mozilla::TimeDuration& rel_time)
 {
-  CRITICAL_SECTION* cs = &lock.lock.platformData()->criticalSection;
+  CRITICAL_SECTION* cs = &lock.platformData()->criticalSection;
 
   // Note that DWORD is unsigned, so we have to be careful to clamp at 0.
   // If rel_time is Forever, then ToMilliseconds is +inf, which evaluates as
@@ -82,13 +82,13 @@ js::ConditionVariable::wait_for(UniqueLock<Mutex>& lock,
   return CVStatus::Timeout;
 }
 
-js::ConditionVariable::~ConditionVariable()
+js::detail::ConditionVariableImpl::~ConditionVariableImpl()
 {
   // Native condition variables don't require cleanup.
 }
 
-inline js::ConditionVariable::PlatformData*
-js::ConditionVariable::platformData()
+inline js::detail::ConditionVariableImpl::PlatformData*
+js::detail::ConditionVariableImpl::platformData()
 {
   static_assert(sizeof platformData_ >= sizeof(PlatformData),
                 "platformData_ is too small");