diff --git a/BUILD.gn b/BUILD.gn
index f1ac0bb32b..f299446d45 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -361,6 +361,13 @@ config("common_config") {
     # Used in Chromium's overrides to disable logging
     defines += [ "WEBRTC_UNSAFE_FUZZER_MODE" ]
   }
+
+  if (!build_with_chromium && rtc_win_undef_unicode) {
+    cflags += [
+      "/UUNICODE",
+      "/U_UNICODE",
+    ]
+  }
 }
 
 config("common_objc") {
diff --git a/tools_webrtc/mb/mb_config.pyl b/tools_webrtc/mb/mb_config.pyl
index e468bb0c95..b452f74ee2 100644
--- a/tools_webrtc/mb/mb_config.pyl
+++ b/tools_webrtc/mb/mb_config.pyl
@@ -99,7 +99,7 @@
         'dummy_audio_file_devices_no_protobuf':
           'dummy_audio_file_devices_no_protobuf_x86',
         'rtti_no_sctp':
-          'rtti_no_sctp_x86',
+          'rtti_no_sctp_no_unicode_win_x86',
       },
     },
     'client.webrtc.perf': {
@@ -241,7 +241,7 @@
         'dummy_audio_file_devices_no_protobuf':
           'dummy_audio_file_devices_no_protobuf_x86',
         'rtti_no_sctp':
-          'rtti_no_sctp_x86',
+          'rtti_no_sctp_no_unicode_win_x86',
       },
     }
   },
@@ -432,8 +432,8 @@
     'dummy_audio_file_devices_no_protobuf_x86': [
       'debug_bot', 'x86', 'dummy_audio_file_devices', 'no_protobuf'
     ],
-    'rtti_no_sctp_x86': [
-      'debug_bot', 'x86', 'rtti', 'no_sctp'
+    'rtti_no_sctp_no_unicode_win_x86': [
+      'debug_bot', 'x86', 'rtti', 'no_sctp', 'win_undef_unicode'
     ],
 
     'bwe_test_logging_android_arm': [
@@ -627,5 +627,9 @@
     'winuwp': {
       'gn_args': 'target_os="winuwp"',
     },
+
+    'win_undef_unicode': {
+      'gn_args': 'rtc_win_undef_unicode=true',
+    },
   },
 }
diff --git a/webrtc.gni b/webrtc.gni
index 3a89a9a9c7..6ba8d0aeb3 100644
--- a/webrtc.gni
+++ b/webrtc.gni
@@ -187,6 +187,14 @@ declare_args() {
   # (they will still be included in libjingle_peerconnection_so.so and
   # WebRTC.framework)
   rtc_include_builtin_video_codecs = true
+
+  # When set to true and in a standalone build, it will undefine UNICODE and
+  # _UNICODE (which are always defined globally by the Chromium Windows
+  # toolchain).
+  # This is only needed for testing purposes, WebRTC wants to be sure it
+  # doesn't assume /DUNICODE and /D_UNICODE but that it explicitly uses
+  # wide character functions.
+  rtc_win_undef_unicode = false
 }
 
 if (!build_with_mozilla) {