diff --git a/llvm/lib/LTO/LTO.cpp b/llvm/lib/LTO/LTO.cpp
--- a/llvm/lib/LTO/LTO.cpp
+++ b/llvm/lib/LTO/LTO.cpp
@@ -1290,7 +1290,8 @@
         GV->setLinkage(GlobalValue::InternalLinkage);
     }
 
-    RegularLTO.CombinedModule->addModuleFlag(Module::Error, "LTOPostLink", 1);
+    if (!RegularLTO.CombinedModule->getModuleFlag("LTOPostLink"))
+      RegularLTO.CombinedModule->addModuleFlag(Module::Error, "LTOPostLink", 1);
 
     if (Conf.PostInternalizeModuleHook &&
         !Conf.PostInternalizeModuleHook(0, *RegularLTO.CombinedModule))
diff --git a/llvm/lib/LTO/LTOCodeGenerator.cpp b/llvm/lib/LTO/LTOCodeGenerator.cpp
--- a/llvm/lib/LTO/LTOCodeGenerator.cpp
+++ b/llvm/lib/LTO/LTOCodeGenerator.cpp
@@ -618,7 +618,8 @@
   this->applyScopeRestrictions();
 
   // Write LTOPostLink flag for passes that require all the modules.
-  MergedModule->addModuleFlag(Module::Error, "LTOPostLink", 1);
+  if (!MergedModule->getModuleFlag("LTOPostLink"))
+    MergedModule->addModuleFlag(Module::Error, "LTOPostLink", 1);
 
   // Add an appropriate DataLayout instance for this module...
   MergedModule->setDataLayout(TargetMach->createDataLayout());
diff --git a/llvm/test/LTO/ARM/lto-linking-metadata-already-present.ll b/llvm/test/LTO/ARM/lto-linking-metadata-already-present.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/LTO/ARM/lto-linking-metadata-already-present.ll
@@ -0,0 +1,24 @@
+; RUN: opt %s -o %t1.bc
+
+; RUN: llvm-lto %t1.bc -o %t1.save.opt -save-linked-module -save-merged-module -O1 --exported-symbol=foo
+; RUN: llvm-dis < %t1.save.opt.merged.bc | FileCheck %s
+
+; RUN: llvm-lto2 run %t1.bc -o %t.out.o -save-temps \
+; RUN:     -r=%t1.bc,foo,pxl
+; RUN: llvm-dis < %t.out.o.0.2.internalize.bc | FileCheck  %s
+
+; Tests that LTO won't add LTOPostLink twice.
+
+target datalayout = "e-m:e-p:32:32-Fi8-i64:64-v128:64:128-a:0:32-n32-S64"
+target triple = "armv7a-unknown-linux"
+
+define void @foo() {
+entry:
+  ret void
+}
+
+!llvm.module.flags = !{!1}
+!1 = !{i32 1, !"LTOPostLink", i32 1}
+
+; CHECK: !llvm.module.flags = !{[[MD_NUM:![0-9]+]]}
+; CHECK: [[MD_NUM]] = !{i32 1, !"LTOPostLink", i32 1}