diff --git a/lld/MachO/SymbolTable.h b/lld/MachO/SymbolTable.h
--- a/lld/MachO/SymbolTable.h
+++ b/lld/MachO/SymbolTable.h
@@ -72,6 +72,7 @@
 };
 
 void reportPendingUndefinedSymbols();
+void reportPendingDuplicateSymbols();
 
 // Call reportPendingUndefinedSymbols() to emit diagnostics.
 void treatUndefinedSymbol(const Undefined &, StringRef source);
diff --git a/lld/MachO/SymbolTable.cpp b/lld/MachO/SymbolTable.cpp
--- a/lld/MachO/SymbolTable.cpp
+++ b/lld/MachO/SymbolTable.cpp
@@ -45,6 +45,17 @@
   return {sym, p.second};
 }
 
+namespace {
+struct DuplicateSymbolReporter {
+  const Symbol *sym;
+  const std::string errorMessage;
+
+  DuplicateSymbolReporter(const Symbol *sym, const std::string errorMessage)
+      : sym(sym), errorMessage(errorMessage) {}
+};
+std::vector<DuplicateSymbolReporter> dupSymReporter;
+} // namespace
+
 Defined *SymbolTable::addDefined(StringRef name, InputFile *file,
                                  InputSection *isec, uint64_t value,
                                  uint64_t size, bool isWeakDef,
@@ -90,7 +101,7 @@
         message += toString(defined->getFile()) + "\n>>> defined in ";
         if (!src2.empty())
           message += src2 + "\n>>>            ";
-        error(message + toString(file));
+        dupSymReporter.push_back({defined, message + toString(file)});
       }
 
     } else if (auto *dysym = dyn_cast<DylibSymbol>(s)) {
@@ -366,6 +377,12 @@
 MapVector<const Undefined *, UndefinedDiag> undefs;
 }
 
+void macho::reportPendingDuplicateSymbols() {
+  for (const auto &duplicate : dupSymReporter)
+    if (duplicate.sym->isLive())
+      error(duplicate.errorMessage);
+}
+
 void macho::reportPendingUndefinedSymbols() {
   for (const auto &undef : undefs) {
     const UndefinedDiag &locations = undef.second;
diff --git a/lld/MachO/Writer.cpp b/lld/MachO/Writer.cpp
--- a/lld/MachO/Writer.cpp
+++ b/lld/MachO/Writer.cpp
@@ -1185,8 +1185,9 @@
   if (in.initOffsets->isNeeded())
     in.initOffsets->setUp();
 
-  // Do not proceed if there was an undefined symbol.
+  // Do not proceed if there were undefined or duplicate symbols.
   reportPendingUndefinedSymbols();
+  reportPendingDuplicateSymbols();
   if (errorCount())
     return;
 
diff --git a/lld/test/MachO/abs-duplicate.s b/lld/test/MachO/abs-duplicate.s
new file mode 100644
--- /dev/null
+++ b/lld/test/MachO/abs-duplicate.s
@@ -0,0 +1,40 @@
+# REQUIRES: x86
+# RUN: rm -rf %t; split-file %s %t
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/test.s -o %t/test.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/weakfoo.s -o %t/weakfoo.o
+# RUN: not %lld -lSystem %t/test.o %t/weakfoo.o -o /dev/null 2>&1 | FileCheck %s
+
+# CHECK:      error: duplicate symbol: _weakfoo
+# CHECK-NEXT: >>> defined in {{.*}}/test.o
+# CHECK-NEXT: >>> defined in {{.*}}/weakfoo.o
+
+## Duplicate absolute symbols that will be dead stripped later should not fail.
+# RUN: %lld -lSystem -dead_strip -map %t/stripped-duplicate-map %t/test.o %t/weakfoo.o -o %t/test
+# RUN: llvm-objdump --syms %t/test | FileCheck %s --check-prefix=DUP
+# DUP-LABEL: SYMBOL TABLE:
+# DUP-NEXT:   g F __TEXT,__text _main
+# DUP-NEXT:   g F __TEXT,__text __mh_execute_header
+# DUP-NEXT:   *UND* dyld_stub_binder
+
+## Dead stripped non-section symbols don't show up in map files because there's no input section.
+## Check that _weakfoo doesn't show up. This matches ld64.
+# RUN: FileCheck --check-prefix=DUPMAP %s < %t/stripped-duplicate-map
+# DUPMAP: _main
+# DUPMAP-LABEL: Dead Stripped Symbols
+# DUPMAP-NOT: _weakfoo
+
+#--- weakfoo.s
+.globl _weakfoo
+## The weak attribute is ignored for absolute symbols, so we will have a
+## duplicate symbol error for _weakfoo.
+.weak_definition _weakfoo
+_weakfoo = 0x1234
+
+#--- test.s
+.globl _main, _weakfoo
+.weak_definition _weakfoo
+_weakfoo = 0x5678
+
+.text
+_main:
+  ret
diff --git a/lld/test/MachO/dead-strip.s b/lld/test/MachO/dead-strip.s
--- a/lld/test/MachO/dead-strip.s
+++ b/lld/test/MachO/dead-strip.s
@@ -321,7 +321,6 @@
 # RUN: %lld -dylib -dead_strip --deduplicate-literals %t/literals.o -o %t/literals
 # RUN: llvm-objdump --macho --section="__TEXT,__cstring" --section="__DATA,str_ptrs" \
 # RUN:   --section="__TEXT,__literals" %t/literals | FileCheck %s --check-prefix=LIT
-
 # LIT:      Contents of (__TEXT,__cstring) section
 # LIT-NEXT: foobar
 # LIT-NEXT: Contents of (__DATA,str_ptrs) section
@@ -330,6 +329,44 @@
 # LIT-NEXT: Contents of (__TEXT,__literals) section
 # LIT-NEXT: ef be ad de {{$}}
 
+## Duplicate symbols that will be dead stripped later should not fail.
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-macos \
+# RUN:     %t/duplicate1.s -o %t/duplicate1.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-macos \
+# RUN:     %t/duplicate2.s -o %t/duplicate2.o
+# RUN: %lld -lSystem -dead_strip -map %t/stripped-duplicate-map %t/duplicate1.o \
+# RUN:     %t/duplicate2.o -o %t/duplicate
+# RUN: llvm-objdump --syms %t/duplicate | FileCheck %s --check-prefix=DUP
+# DUP-LABEL: SYMBOL TABLE:
+# DUP-NEXT:   g F __TEXT,__text _main
+# DUP-NEXT:   g F __TEXT,__text __mh_execute_header
+# DUP-NEXT:   *UND* dyld_stub_binder
+
+## Check that the duplicate dead stripped symbols get listed properly.
+# RUN: FileCheck --check-prefix=DUPMAP %s < %t/stripped-duplicate-map
+# DUPMAP: _main
+# DUPMAP-LABEL: Dead Stripped Symbols
+# DUPMAP: <<dead>> [ 2] _foo
+
+#--- duplicate1.s
+.text
+.globl _main, _foo
+_foo:
+  retq
+
+_main:
+  retq
+
+.subsections_via_symbols
+
+#--- duplicate2.s
+.text
+.globl _foo
+_foo:
+  retq
+
+.subsections_via_symbols
+
 #--- basics.s
 .comm _ref_com, 1
 .comm _unref_com, 1
diff --git a/lld/test/MachO/invalid/abs-duplicate.s b/lld/test/MachO/invalid/abs-duplicate.s
deleted file mode 100644
--- a/lld/test/MachO/invalid/abs-duplicate.s
+++ /dev/null
@@ -1,25 +0,0 @@
-# REQUIRES: x86
-# RUN: rm -rf %t; split-file %s %t
-# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/test.s -o %t/test.o
-# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/weakfoo.s -o %t/weakfoo.o
-# RUN: not %lld -lSystem %t/test.o %t/weakfoo.o -o %t/test 2>&1 | FileCheck %s
-
-# CHECK:      error: duplicate symbol: _weakfoo
-# CHECK-NEXT: >>> defined in {{.*}}/test.o
-# CHECK-NEXT: >>> defined in {{.*}}/weakfoo.o
-
-#--- weakfoo.s
-.globl _weakfoo
-## The weak attribute is ignored for absolute symbols, so we will have a
-## duplicate symbol error for _weakfoo.
-.weak_definition _weakfoo
-_weakfoo = 0x1234
-
-#--- test.s
-.globl _main, _weakfoo
-.weak_definition _weakfoo
-_weakfoo = 0x5678
-
-.text
-_main:
-  ret