diff -up chromium-91.0.4472.77/build/config/compiler/BUILD.gn.aarch-cxxflags chromium-91.0.4472.77/build/config/compiler/BUILD.gn
--- chromium-91.0.4472.77/build/config/compiler/BUILD.gn.aarch-cxxflags	2021-06-02 12:58:21.998750145 -0400
+++ chromium-91.0.4472.77/build/config/compiler/BUILD.gn	2021-06-02 12:59:29.762092189 -0400
@@ -1511,6 +1511,10 @@ config("default_warnings") {
       cflags += [ "-Wno-psabi" ]
     }
 
+    if (current_cpu == "arm64" && !is_clang) {
+      cflags_cc += [ "-flax-vector-conversions" ]
+    }
+
     if (!is_clang) {
       cflags_cc += [
         # See comment for -Wno-c++11-narrowing.