diff --git a/src/platform-tls-mac.h b/src/platform-tls-mac.h
new file mode 100644
index 0000000000..86a3347d0f
--- /dev/null
+++ b/src/platform-tls-mac.h
@@ -0,0 +1,62 @@
+// Copyright 2011 the V8 project authors. All rights reserved.
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+//       notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+//       copyright notice, this list of conditions and the following
+//       disclaimer in the documentation and/or other materials provided
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#ifndef V8_PLATFORM_TLS_MAC_H_
+#define V8_PLATFORM_TLS_MAC_H_
+
+#include "globals.h"
+
+namespace v8 {
+namespace internal {
+
+#if defined(V8_HOST_ARCH_IA32) || defined(V8_HOST_ARCH_X64)
+
+#define V8_FAST_TLS_SUPPORTED 1
+
+INLINE(intptr_t InternalGetExistingThreadLocal(intptr_t index));
+
+inline intptr_t InternalGetExistingThreadLocal(intptr_t index) {
+  // The constants below are taken from pthreads.s from the XNU kernel
+  // sources archive at www.opensource.apple.com.
+  intptr_t result;
+#if defined(V8_HOST_ARCH_IA32)
+  asm("movl %%gs:0x48(,%1,4), %0;"
+      :"=r"(result)  // Output must be a writable register.
+      :"0"(index));  // Input is the same as output.
+#else
+  asm("movq %%gs:0x60(,%1,8), %0;"
+      :"=r"(result)
+      :"0"(index));
+#endif
+  return result;
+}
+
+#endif
+
+} }  // namespace v8::internal
+
+#endif  // V8_PLATFORM_TLS_MAC_H_
diff --git a/src/platform-tls.h b/src/platform-tls.h
index a7c40e567e..564917540b 100644
--- a/src/platform-tls.h
+++ b/src/platform-tls.h
@@ -41,6 +41,8 @@
 
 #if defined(_MSC_VER) && (defined(_WIN32) || defined(_WIN64))
 #include "platform-tls-win32.h"
+#elif defined(__APPLE__)
+#include "platform-tls-mac.h"
 #endif
 
 #endif
diff --git a/tools/gyp/v8.gyp b/tools/gyp/v8.gyp
index 0d3b5cdb26..88044540d3 100644
--- a/tools/gyp/v8.gyp
+++ b/tools/gyp/v8.gyp
@@ -438,6 +438,7 @@
             '../../src/objects.h',
             '../../src/parser.cc',
             '../../src/parser.h',
+            '../../src/platform-tls-mac.h',
             '../../src/platform-tls-win32.h',
             '../../src/platform-tls.h',
             '../../src/platform.h',
diff --git a/tools/v8.xcodeproj/project.pbxproj b/tools/v8.xcodeproj/project.pbxproj
index 1884199cab..386e7f01c6 100644
--- a/tools/v8.xcodeproj/project.pbxproj
+++ b/tools/v8.xcodeproj/project.pbxproj
@@ -915,6 +915,7 @@
 		89FB0E360F8E531900B04B3C /* d8-posix.cc */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; name = "d8-posix.cc"; path = "../src/d8-posix.cc"; sourceTree = "<group>"; };
 		89FB0E370F8E531900B04B3C /* d8-windows.cc */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; name = "d8-windows.cc"; path = "../src/d8-windows.cc"; sourceTree = "<group>"; };
 		9C1F8E1D133906180068B362 /* small-pointer-list.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = "small-pointer-list.h"; sourceTree = "<group>"; };
+		9C76176D133FB7740057370B /* platform-tls-mac.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = "platform-tls-mac.h"; sourceTree = "<group>"; };
 		9C8E8061133CF772004058A5 /* platform-tls.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = "platform-tls.h"; sourceTree = "<group>"; };
 		9F11D99E105AF0A300EBE5B2 /* heap-profiler.cc */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = "heap-profiler.cc"; sourceTree = "<group>"; };
 		9F11D99F105AF0A300EBE5B2 /* heap-profiler.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = "heap-profiler.h"; sourceTree = "<group>"; };
@@ -1239,6 +1240,7 @@
 				897FF1670E719B8F00D62E90 /* platform-macos.cc */,
 				897FF1680E719B8F00D62E90 /* platform-nullos.cc */,
 				893A72230F7B0FF200303DD2 /* platform-posix.cc */,
+				9C76176D133FB7740057370B /* platform-tls-mac.h */,
 				9C8E8061133CF772004058A5 /* platform-tls.h */,
 				897FF1690E719B8F00D62E90 /* platform-win32.cc */,
 				897FF16A0E719B8F00D62E90 /* platform.h */,