diff --git a/webrtc/build/gyp_webrtc b/webrtc/build/gyp_webrtc
index 5945b95cf9..3ca64d94de 100755
--- a/webrtc/build/gyp_webrtc
+++ b/webrtc/build/gyp_webrtc
@@ -90,18 +90,6 @@ if __name__ == '__main__':
                gyp_chromium.additional_include_files(supplemental_includes,
                                                      args)])
 
-  # Set target_subarch for iOS builds if not already set.
-  if gyp_vars.get('OS') == 'ios' and 'target_subarch' not in gyp_vars:
-    os.environ.setdefault('GYP_DEFINES', '')
-    target_subarch = None
-    if gyp_vars.get('target_arch') in ('arm', 'ia32'):
-      target_subarch = 'arm32'
-    elif gyp_vars.get('target_arch') in ('arm64', 'x64'):
-      target_subarch = 'arm64'
-    if target_subarch:
-      print 'INFO: Appending target_subarch=%s to GYP_DEFINES' % target_subarch
-      os.environ['GYP_DEFINES'] += ' target_subarch=%s' % target_subarch
-
   # Set the gyp depth variable to the root of the checkout.
   args.append('--depth=' + os.path.relpath(checkout_root))
 
diff --git a/webrtc/supplement.gypi b/webrtc/supplement.gypi
index d66b828177..075e2adb06 100644
--- a/webrtc/supplement.gypi
+++ b/webrtc/supplement.gypi
@@ -9,6 +9,17 @@
       ['OS=="ios"', {
         # Default to using BoringSSL on iOS.
         'use_openssl%': 1,
+
+        # Set target_subarch for if not already set. This is needed because the
+        # Chromium iOS toolchain relies on target_subarch being set.
+        'conditions': [
+          ['target_arch=="arm" or target_arch=="ia32"', {
+            'target_subarch%': 'arm32',
+          }],
+          ['target_arch=="arm64" or target_arch=="x64"', {
+            'target_subarch%': 'arm64',
+          }],
+        ],
       }],
     ],
   },