diff --git a/webrtc/base/base.gyp b/webrtc/base/base.gyp
index 9e55efc807..3efcf69c6b 100644
--- a/webrtc/base/base.gyp
+++ b/webrtc/base/base.gyp
@@ -475,7 +475,7 @@
             ],
           },
         }],
-        ['OS=="mac" or OS=="ios"', {
+        ['(OS=="mac" or OS=="ios") and nacl_untrusted_build==0', {
           'sources': [
             'maccocoathreadhelper.h',
             'maccocoathreadhelper.mm',
@@ -555,7 +555,7 @@
             }],
           ],
         }],
-        ['OS=="win"', {
+        ['OS=="win" and nacl_untrusted_build==0', {
           'sources': [
             'win32.cc',
             'win32.h',
diff --git a/webrtc/build/common.gypi b/webrtc/build/common.gypi
index 26acf4b5e2..37f8ead389 100644
--- a/webrtc/build/common.gypi
+++ b/webrtc/build/common.gypi
@@ -95,6 +95,10 @@
     # third party code will still have the reduced warning settings.
     'chromium_code': 1,
 
+    # Targets are by default not NaCl untrusted code. Use this variable exclude
+    # code that uses libraries that aren't available in the NaCl sandbox.
+    'nacl_untrusted_build%': 0,
+
     # Set to 1 to enable code coverage on Linux using the gcov library.
     'coverage%': 0,