Index: lib/LTO/LTO.cpp
===================================================================
--- lib/LTO/LTO.cpp
+++ lib/LTO/LTO.cpp
@@ -82,10 +82,6 @@
         isPrevailing,
     function_ref<void(StringRef, GlobalValue::GUID, GlobalValue::LinkageTypes)>
         recordNewLinkage) {
-  if (Index.modulePaths().size() == 1)
-    // Nothing to do if we don't have multiple modules
-    return;
-
   // We won't optimize the globals that are referenced by an alias for now
   // Ideally we should turn the alias into a global and duplicate the definition
   // when needed.
Index: test/ThinLTO/X86/weak_resolution_single.ll
===================================================================
--- /dev/null
+++ test/ThinLTO/X86/weak_resolution_single.ll
@@ -0,0 +1,9 @@
+; RUN: opt -module-summary %s -o %t.bc
+; RUN: llvm-lto -thinlto-action=thinlink -o %t2.bc %t.bc
+
+; RUN: llvm-lto -thinlto-action=promote %t.bc -thinlto-index=%t2.bc -exported-symbol=foo -o - | llvm-lto -thinlto-action=internalize -thinlto-module-id=%t.bc - -thinlto-index=%t2.bc -exported-symbol=foo -o - | llvm-dis -o - | FileCheck %s
+
+; CHECK: define weak_odr void @foo()
+define linkonce_odr void @foo() {
+  ret void
+}