Index: lib/LTO/LTO.cpp
===================================================================
--- lib/LTO/LTO.cpp
+++ lib/LTO/LTO.cpp
@@ -455,6 +455,7 @@
   auto *ResI = Res.begin();
   auto *ResE = Res.end();
   (void)ResE;
+  std::vector<StringRef> ForcePrevailing;
   for (const InputFile::Symbol &Sym : Syms) {
     assert(ResI != ResE);
     SymbolResolution Res = *ResI++;
@@ -491,6 +492,8 @@
         (GlobalRes.Partition != GlobalResolution::Unknown &&
          GlobalRes.Partition != Partition)) {
       GlobalRes.Partition = GlobalResolution::External;
+      if (Sym.isWeak() && !Sym.isExecutable())
+        ForcePrevailing.push_back(Name);
     } else
       // First recorded reference, save the current partition.
       GlobalRes.Partition = Partition;
@@ -500,6 +503,9 @@
     GlobalRes.VisibleOutsideSummary |=
         (Res.VisibleToRegularObj || Sym.isUsed() || !InSummary);
   }
+
+  for (auto Name : ForcePrevailing)
+    GlobalResolutions[Name].Prevailing = true;
 }
 
 static void writeToResolutionFile(raw_ostream &OS, InputFile *Input,
Index: test/ThinLTO/X86/externally-visible-linkonce.ll
===================================================================
--- test/ThinLTO/X86/externally-visible-linkonce.ll
+++ test/ThinLTO/X86/externally-visible-linkonce.ll
@@ -0,0 +1,32 @@
+; RUN: opt -module-summary %s -o %t.bc
+; RUN: llvm-lto2 run -save-temps %t.bc -o %t.out \
+; RUN:               -r=%t.bc,_ZL5initSv,plx \
+; RUN:               -r=%t.bc,_ZN9SingletonI1SE11getInstanceEv,lx \
+; RUN:               -r=%t.bc,_ZZN9SingletonI1SE11getInstanceEvE8instance,lx
+; RUN: llvm-dis %t.out.1.1.promote.bc -o - | FileCheck %s
+
+; CHECK: @_ZZN9SingletonI1SE11getInstanceEvE8instance = available_externally dso_local global %struct.S zeroinitializer
+; CHECK: define internal dereferenceable(16) %struct.S* @_ZN9SingletonI1SE11getInstanceEv() comdat
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+%struct.S = type { i64, i64 }
+
+$_ZN9SingletonI1SE11getInstanceEv = comdat any
+
+$_ZZN9SingletonI1SE11getInstanceEvE8instance = comdat any
+
+@_ZZN9SingletonI1SE11getInstanceEvE8instance = linkonce_odr dso_local global %struct.S zeroinitializer, comdat, align 8
+
+define dso_local void @_ZL5initSv() {
+  %1 = call dereferenceable(16) %struct.S* @_ZN9SingletonI1SE11getInstanceEv()
+  %2 = getelementptr inbounds %struct.S, %struct.S* %1, i32 0, i32 0
+  store i64 1, i64* %2, align 8
+  ret void
+}
+
+define linkonce_odr dso_local dereferenceable(16) %struct.S* @_ZN9SingletonI1SE11getInstanceEv() #0 comdat align 2 {
+  ret %struct.S* @_ZZN9SingletonI1SE11getInstanceEvE8instance
+}
+