diff --git a/tools_webrtc/mb/mb_config.pyl b/tools_webrtc/mb/mb_config.pyl
index be6869e7c5..7bb70f4564 100644
--- a/tools_webrtc/mb/mb_config.pyl
+++ b/tools_webrtc/mb/mb_config.pyl
@@ -228,8 +228,7 @@
       'gn', 'ubsan', 'clang', 'openh264_release_bot', 'x64'
     ],
     'ubsan_vptr_clang_release_bot_x64': [
-      'gn', 'ubsan_vptr', 'clang', 'openh264_release_bot', 'x64',
-      'use_default_libcxx'
+      'gn', 'ubsan_vptr', 'clang', 'openh264_release_bot', 'x64'
     ],
     'debug_bot_x86': [
       'gn', 'openh264_debug_bot', 'x86'
diff --git a/tools_webrtc/ubsan/vptr_blacklist.txt b/tools_webrtc/ubsan/vptr_blacklist.txt
index 02adc84630..739de36659 100644
--- a/tools_webrtc/ubsan/vptr_blacklist.txt
+++ b/tools_webrtc/ubsan/vptr_blacklist.txt
@@ -20,3 +20,8 @@ src:*/third_party/protobuf/src/google/protobuf/compiler/plugin.pb.cc
 src:*/third_party/protobuf/src/google/protobuf/compiler/cpp/cpp_message.cc
 src:*/third_party/protobuf/src/google/protobuf/descriptor.pb.cc
 
+#############################################################################
+# UBsan goes into an infinite recursion when __dynamic_cast instrumented with
+# "vptr". See crbug.com/609786.
+
+src:*/third_party/libc\+\+abi/trunk/src/private_typeinfo.cpp