Index: lld/MachO/SyntheticSections.cpp
===================================================================
--- lld/MachO/SyntheticSections.cpp
+++ lld/MachO/SyntheticSections.cpp
@@ -24,6 +24,7 @@
 #include "llvm/Support/LEB128.h"
 #include "llvm/Support/Parallel.h"
 #include "llvm/Support/Path.h"
+#include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/Support/xxhash.h"
 
 #if defined(__APPLE__)
@@ -1208,7 +1209,10 @@
 }
 
 void SymtabSection::finalizeContents() {
+  SmallPtrSet<const Symbol*, 8> seenSymbols;
   auto addSymbol = [&](std::vector<SymtabEntry> &symbols, Symbol *sym) {
+    if (seenSymbols.insert(sym).second != true)
+      return;
     uint32_t strx = stringTableSection.addString(sym->getName());
     symbols.push_back({sym, strx});
   };
Index: lld/test/MachO/private-label-alias.s
===================================================================
--- lld/test/MachO/private-label-alias.s
+++ lld/test/MachO/private-label-alias.s
@@ -26,9 +26,11 @@
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/weak-then-private.s -o %t/weak-then-private.o
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/private-then-weak.s -o %t/private-then-weak.o
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/no-dead-strip.s -o %t/no-dead-strip.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/all-local.s -o %t/all-local.o
 # RUN: %lld -dylib %t/weak-then-private.o %t/private-then-weak.o -o %t/test1
 # RUN: %lld -dylib %t/private-then-weak.o %t/weak-then-private.o -o %t/test2
 # RUN: %lld -dead_strip %t/no-dead-strip.o -o %t/no-dead-strip
+# RUN: %lld -dylib %t/all-local.o -o %t/all-local
 
 # RUN: llvm-objdump --macho --syms --section="__DATA,__data" --weak-bind %t/test1 | FileCheck %s
 # RUN: llvm-objdump --macho --syms --section="__DATA,__data" --weak-bind %t/test2 | FileCheck %s
@@ -59,6 +61,13 @@
 # RUN:   --check-prefix=NO-DEAD-STRIP
 # NO-DEAD-STRIP: __data        00000010
 
+## Ensure that a private alias to a local label doesn't write two identical
+## entries to the symbol table.
+# RUN: llvm-objdump --macho --syms %t/all-local | FileCheck %s --check-prefix=NO-DUPES
+# NO-DUPES: SYMBOL TABLE:
+# NO-DUPES-NEXT: 00000000000002c8 l     F __TEXT,__text _label
+# NO-DUPES-NEXT: 00000000000002d0 l     F __TEXT,__text _ref
+
 #--- weak-then-private.s
 .globl _weak
 .weak_definition _weak
@@ -103,3 +112,15 @@
   .quad 0x123
 
 .subsections_via_symbols
+
+#--- all-local.s
+.text
+
+l_ignored:
+_label:
+  .quad 0x123
+
+_ref:
+  .quad l_ignored
+
+.subsections_via_symbols