diff --git a/clang/lib/CodeGen/BackendUtil.cpp b/clang/lib/CodeGen/BackendUtil.cpp
index 2d959827d6972..d28d886b3551e 100644
--- a/clang/lib/CodeGen/BackendUtil.cpp
+++ b/clang/lib/CodeGen/BackendUtil.cpp
@@ -1199,7 +1199,8 @@ void EmitAssemblyHelper::RunOptimizationPipeline(
       }
     }
 
-    if (shouldEmitUnifiedLTOModueFlag())
+    if (shouldEmitUnifiedLTOModueFlag() &&
+        !TheModule->getModuleFlag("UnifiedLTO"))
       TheModule->addModuleFlag(llvm::Module::Error, "UnifiedLTO", uint32_t(1));
   }
 
diff --git a/clang/test/CodeGen/unified-lto-module-flag.ll b/clang/test/CodeGen/unified-lto-module-flag.ll
new file mode 100644
index 0000000000000..deefe826d1566
--- /dev/null
+++ b/clang/test/CodeGen/unified-lto-module-flag.ll
@@ -0,0 +1,11 @@
+; Test that we do not duplicate the UnifiedLTO module flag.
+;
+; RUN: %clang_cc1 -emit-llvm -flto=full -funified-lto -o - %s | FileCheck %s
+
+; CHECK: !llvm.module.flags = !{!0, !1, !2, !3}
+!llvm.module.flags = !{!0, !1, !2, !3}
+
+!0 = !{i32 1, !"wchar_size", i32 2}
+!1 = !{i32 7, !"frame-pointer", i32 2}
+!2 = !{i32 1, !"EnableSplitLTOUnit", i32 1}
+!3 = !{i32 1, !"UnifiedLTO", i32 1}