diff --git a/llvm/lib/Transforms/IPO/ConstantMerge.cpp b/llvm/lib/Transforms/IPO/ConstantMerge.cpp
--- a/llvm/lib/Transforms/IPO/ConstantMerge.cpp
+++ b/llvm/lib/Transforms/IPO/ConstantMerge.cpp
@@ -105,6 +105,8 @@
     return CanMerge::No;
   if (hasMetadataOtherThanDebugLoc(Old))
     return CanMerge::No;
+  if (Old->getThreadLocalMode() != New->getThreadLocalMode())
+    return CanMerge::No;
   assert(!hasMetadataOtherThanDebugLoc(New));
   if (!Old->hasGlobalUnnamedAddr())
     New->setUnnamedAddr(GlobalValue::UnnamedAddr::None);
diff --git a/llvm/test/Transforms/ConstantMerge/dont-merge.ll b/llvm/test/Transforms/ConstantMerge/dont-merge.ll
--- a/llvm/test/Transforms/ConstantMerge/dont-merge.ll
+++ b/llvm/test/Transforms/ConstantMerge/dont-merge.ll
@@ -80,3 +80,15 @@
         store i32* @T4D2, i32** %P8
         ret void
 }
+
+; CHECK: @T5tls
+; CHECK: @T5ua
+
+@T5tls = private thread_local constant i32 555
+@T5ua = private unnamed_addr constant i32 555
+
+define void @test5(i32** %P1, i32** %P2) {
+        store i32* @T5tls, i32** %P1
+        store i32* @T5ua, i32** %P2
+        ret void
+}