diff --git a/tools_webrtc/mb/mb_config.pyl b/tools_webrtc/mb/mb_config.pyl
index de92c51c02..c90a406806 100644
--- a/tools_webrtc/mb/mb_config.pyl
+++ b/tools_webrtc/mb/mb_config.pyl
@@ -536,8 +536,7 @@
     },
 
     'msan': {
-      'gn_args': ('is_msan=true msan_track_origins=2 '
-                  'use_prebuilt_instrumented_libraries=true'),
+      'gn_args': 'is_msan=true msan_track_origins=2',
     },
 
     'no_clang': {