diff --git a/lld/MachO/Config.h b/lld/MachO/Config.h
--- a/lld/MachO/Config.h
+++ b/lld/MachO/Config.h
@@ -148,6 +148,7 @@
   bool deadStripDylibs = false;
   bool demangle = false;
   bool deadStrip = false;
+  bool errorForArchMismatch = false;
   PlatformInfo platformInfo;
   NamespaceKind namespaceKind = NamespaceKind::twolevel;
   UndefinedSymbolTreatment undefinedSymbolTreatment =
diff --git a/lld/MachO/Driver.cpp b/lld/MachO/Driver.cpp
--- a/lld/MachO/Driver.cpp
+++ b/lld/MachO/Driver.cpp
@@ -1226,6 +1226,7 @@
   config->printWhyLoad = args.hasArg(OPT_why_load);
   config->omitDebugInfo = args.hasArg(OPT_S);
   config->outputType = getOutputType(args);
+  config->errorForArchMismatch = args.hasArg(OPT_arch_errors_fatal);
   if (const Arg *arg = args.getLastArg(OPT_bundle_loader)) {
     if (config->outputType != MH_BUNDLE)
       error("-bundle_loader can only be used with MachO bundle output");
diff --git a/lld/MachO/InputFiles.cpp b/lld/MachO/InputFiles.cpp
--- a/lld/MachO/InputFiles.cpp
+++ b/lld/MachO/InputFiles.cpp
@@ -789,9 +789,18 @@
 
   Architecture arch = getArchitectureFromCpuType(hdr->cputype, hdr->cpusubtype);
   if (arch != config->arch()) {
-    error(toString(this) + " has architecture " + getArchitectureName(arch) +
-          " which is incompatible with target architecture " +
-          getArchitectureName(config->arch()));
+    auto post = [&](bool fail, const Twine &message) -> void {
+      if (fail)
+        error(message);
+      else
+        warn(message);
+    };
+
+    post(config->errorForArchMismatch,
+         toString(this) + " has architecture " + getArchitectureName(arch) +
+             " which is incompatible with target architecture " +
+             getArchitectureName(config->arch()));
+
     return;
   }
 
diff --git a/lld/MachO/Options.td b/lld/MachO/Options.td
--- a/lld/MachO/Options.td
+++ b/lld/MachO/Options.td
@@ -862,7 +862,6 @@
     Group<grp_rare>;
 def arch_errors_fatal : Flag<["-"], "arch_errors_fatal">,
     HelpText<"Escalate to errors any warnings about inputs whose architecture does not match the -arch option">,
-    Flags<[HelpHidden]>,
     Group<grp_rare>;
 def e : Separate<["-"], "e">,
     MetaVarName<"<symbol>">,
diff --git a/lld/test/MachO/invalid/incompatible-arch.s b/lld/test/MachO/invalid/incompatible-arch.s
--- a/lld/test/MachO/invalid/incompatible-arch.s
+++ b/lld/test/MachO/invalid/incompatible-arch.s
@@ -3,8 +3,12 @@
 # RUN: rm -rf %t && mkdir -p %t
 
 # RUN: llvm-mc -filetype=obj -triple=arm64-apple-darwin %s -o %t/test.o
-# RUN: not %lld -arch x86_64 -lSystem %t/test.o -o /dev/null 2>&1 | FileCheck %s -DFILE=%t/test.o
-# CHECK: error: {{.*}}[[FILE]] has architecture arm64 which is incompatible with target architecture x86_64
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t/native.o
+# RUN: not %no_fatal_warnings_lld -arch x86_64 -lSystem %t/test.o -o /dev/null -arch_errors_fatal 2>&1 | FileCheck %s -DFILE=%t/test.o --check-prefix=CHECK-ERROR
+# RUN: %no_fatal_warnings_lld -arch x86_64 -lSystem %t/test.o %t/native.o -o /dev/null 2>&1 | FileCheck %s -DFILE=%t/test.o --check-prefix=CHECK-WARNING
+# RUN: %lld -arch arm64 -lSystem %t/test.o -arch_errors_fatal -o /dev/null
+# CHECK-ERROR: error: {{.*}}[[FILE]] has architecture arm64 which is incompatible with target architecture x86_64
+# CHECK-WARNING: warning: {{.*}}[[FILE]] has architecture arm64 which is incompatible with target architecture x86_64
 
 # RUN: %lld -dylib -arch arm64 -platform_version macOS 10.14 10.15 -o %t/out.dylib %t/test.o
 
@@ -30,7 +34,7 @@
 # RUN:  -o /dev/null 2>&1 | FileCheck %s --check-prefix=OBJ-VERSION
 # OBJ-VERSION: warning: {{.*}}test_x86.o has version 10.15.0, which is newer than target minimum of 10.14.0
 
-## Test that simulators platforms are compat with their simulatees.		
+## Test that simulators platforms are compat with their simulatees.
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-ios14.0 %s -o %t/test_x86_ios.o
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-ios14.0-simulator %s -o %t/test_x86_ios_sim.o
 
@@ -43,7 +47,6 @@
 # RUN: not %lld -dylib  -platform_version watchos-simulator 14.0.0 14.0.0 %t/test_x86_ios_sim.o \
 # RUN:	-o /dev/null 2>&1 | FileCheck %s --check-prefix=CROSS-SIM2
 # CROSS-SIM2: {{.*}}test_x86_ios_sim.o has platform iOS Simulator, which is different from target platform watchOS Simulator
-	
 
 .globl _main
 _main: