diff --git a/js/src/jsapi-tests/testThreadingMutex.cpp b/js/src/jsapi-tests/testThreadingMutex.cpp
index f0d3d408e418..ed5e8833fa32 100644
--- a/js/src/jsapi-tests/testThreadingMutex.cpp
+++ b/js/src/jsapi-tests/testThreadingMutex.cpp
@@ -34,17 +34,3 @@ BEGIN_TEST(testThreadingUnlockGuard)
     return true;
 }
 END_TEST(testThreadingUnlockGuard)
-
-BEGIN_TEST(testThreadingMoveMutex)
-{
-    js::Mutex mutex;
-    mutex.lock();
-    mutex.unlock();
-
-    js::Mutex another(mozilla::Move(mutex));
-    another.lock();
-    another.unlock();
-
-    return true;
-}
-END_TEST(testThreadingMoveMutex)
diff --git a/js/src/threading/Mutex.h b/js/src/threading/Mutex.h
index fae91c3145bf..2640bfc05492 100644
--- a/js/src/threading/Mutex.h
+++ b/js/src/threading/Mutex.h
@@ -7,12 +7,7 @@
 #ifndef threading_Mutex_h
 #define threading_Mutex_h
 
-#include <new>
-#include <string.h>
-
-#include "mozilla/Assertions.h"
 #include "mozilla/Attributes.h"
-#include "mozilla/Move.h"
 
 namespace js {
 
@@ -27,29 +22,28 @@ public:
   void lock();
   void unlock();
 
-  Mutex(Mutex&& rhs)
-    : platformData_(rhs.platformData_)
-  {
-    MOZ_ASSERT(this != &rhs, "self move disallowed!");
-    rhs.platformData_ = nullptr;
-  }
-
-  Mutex& operator=(Mutex&& rhs) {
-    this->~Mutex();
-    new (this) Mutex(mozilla::Move(rhs));
-    return *this;
-  }
-
 private:
   Mutex(const Mutex&) = delete;
   void operator=(const Mutex&) = delete;
+  Mutex(Mutex&&) = delete;
+  void operator=(Mutex&&) = delete;
 
-  PlatformData* platformData() {
-    MOZ_ASSERT(platformData_);
-    return platformData_;
-  };
+  PlatformData* platformData();
 
-  PlatformData* platformData_;
+// Linux and maybe other platforms define the storage size of pthread_mutex_t in
+// bytes. However, we must define it as an array of void pointers to ensure
+// proper alignment.
+#if defined(__APPLE__) && defined(__MACH__) && defined(__i386__)
+  void* platformData_[11];
+#elif defined(__APPLE__) && defined(__MACH__) && defined(__amd64__)
+  void* platformData_[8];
+#elif defined(__linux__)
+  void* platformData_[40 / sizeof(void*)];
+#elif defined(_WIN32)
+  void* platformData_[6];
+#else
+  void* platformData_[64 / sizeof(void*)];
+#endif
 };
 
 } // namespace js
diff --git a/js/src/threading/posix/Mutex.cpp b/js/src/threading/posix/Mutex.cpp
index bef5b2102aab..3e26178edc19 100644
--- a/js/src/threading/posix/Mutex.cpp
+++ b/js/src/threading/posix/Mutex.cpp
@@ -4,32 +4,23 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-#include <pthread.h>
+#include "mozilla/Assertions.h"
 
-#include "js/Utility.h"
+#include <pthread.h>
 
 #include "threading/Mutex.h"
 #include "threading/posix/MutexPlatformData.h"
 
 js::Mutex::Mutex()
 {
-  AutoEnterOOMUnsafeRegion oom;
-  platformData_ = js_new<PlatformData>();
-  if (!platformData_)
-    oom.crash("js::Mutex::Mutex");
-
   int r = pthread_mutex_init(&platformData()->ptMutex, NULL);
   MOZ_RELEASE_ASSERT(r == 0);
 }
 
 js::Mutex::~Mutex()
 {
-  if (!platformData_)
-    return;
-
   int r = pthread_mutex_destroy(&platformData()->ptMutex);
   MOZ_RELEASE_ASSERT(r == 0);
-  js_delete(platformData());
 }
 
 void
@@ -45,3 +36,11 @@ js::Mutex::unlock()
   int r = pthread_mutex_unlock(&platformData()->ptMutex);
   MOZ_RELEASE_ASSERT(r == 0);
 }
+
+js::Mutex::PlatformData*
+js::Mutex::platformData()
+{
+  static_assert(sizeof(platformData_) >= sizeof(PlatformData),
+                "platformData_ is too small");
+  return reinterpret_cast<PlatformData*>(platformData_);
+}
diff --git a/js/src/threading/windows/Mutex.cpp b/js/src/threading/windows/Mutex.cpp
index e3277c314930..ec638100e29c 100644
--- a/js/src/threading/windows/Mutex.cpp
+++ b/js/src/threading/windows/Mutex.cpp
@@ -4,12 +4,11 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
+#include "mozilla/Assertions.h"
 #include "mozilla/DebugOnly.h"
 
 #include "jswin.h"
 
-#include "js/Utility.h"
-
 #include "threading/Mutex.h"
 #include "threading/windows/MutexPlatformData.h"
 
@@ -44,11 +43,6 @@ static MutexNativeImports NativeImports;
 
 js::Mutex::Mutex()
 {
-  AutoEnterOOMUnsafeRegion oom;
-  platformData_ = js_new<PlatformData>();
-  if (!platformData_)
-    oom.crash("js::Mutex::Mutex");
-
   // This number was adopted from NSPR.
   const static DWORD LockSpinCount = 1500;
   BOOL r;
@@ -65,11 +59,7 @@ js::Mutex::Mutex()
 
 js::Mutex::~Mutex()
 {
-  if (!platformData_)
-    return;
-
   DeleteCriticalSection(&platformData()->criticalSection);
-  js_delete(platformData());
 }
 
 void
@@ -83,3 +73,11 @@ js::Mutex::unlock()
 {
   LeaveCriticalSection(&platformData()->criticalSection);
 }
+
+js::Mutex::PlatformData*
+js::Mutex::platformData()
+{
+  static_assert(sizeof(platformData_) >= sizeof(PlatformData),
+                "platformData_ is too small");
+  return reinterpret_cast<PlatformData*>(platformData_);
+}