Index: COFF/SymbolTable.cpp
===================================================================
--- COFF/SymbolTable.cpp
+++ COFF/SymbolTable.cpp
@@ -301,7 +301,8 @@
   std::tie(S, WasInserted) = insert(N);
   if (!isa<BitcodeFile>(F))
     S->IsUsedInRegularObj = true;
-  if (WasInserted || !isa<DefinedRegular>(S))
+  if (WasInserted || (!isa<DefinedRegular>(S) && !isa<DefinedImportThunk>(S) &&
+                      !isa<DefinedImportData>(S)))
     replaceSymbol<DefinedRegular>(S, F, N, /*IsCOMDAT*/ false,
                                   /*IsExternal*/ true, Sym, C);
   else
@@ -317,7 +318,8 @@
   std::tie(S, WasInserted) = insert(N);
   if (!isa<BitcodeFile>(F))
     S->IsUsedInRegularObj = true;
-  if (WasInserted || !isa<DefinedRegular>(S)) {
+  if (WasInserted || (!isa<DefinedRegular>(S) && !isa<DefinedImportThunk>(S) &&
+                      !isa<DefinedImportData>(S))) {
     replaceSymbol<DefinedRegular>(S, F, N, /*IsCOMDAT*/ true,
                                   /*IsExternal*/ true, Sym, nullptr);
     return {S, true};
@@ -334,7 +336,9 @@
   std::tie(S, WasInserted) = insert(N);
   if (!isa<BitcodeFile>(F))
     S->IsUsedInRegularObj = true;
-  if (WasInserted || !isa<DefinedCOFF>(S))
+  if (!WasInserted && (isa<DefinedImportThunk>(S) || isa<DefinedImportData>(S)))
+    reportDuplicate(S, F);
+  else if (WasInserted || !isa<DefinedCOFF>(S))
     replaceSymbol<DefinedCommon>(S, F, N, Size, Sym, C);
   else if (auto *DC = dyn_cast<DefinedCommon>(S))
     if (Size > DC->getSize())
Index: test/COFF/Inputs/otherFunc.s
===================================================================
--- /dev/null
+++ test/COFF/Inputs/otherFunc.s
@@ -0,0 +1,7 @@
+.global otherFunc
+.global MessageBoxA
+.text
+otherFunc:
+  ret
+MessageBoxA:
+  ret
Index: test/COFF/thunk-replace.s
===================================================================
--- /dev/null
+++ test/COFF/thunk-replace.s
@@ -0,0 +1,15 @@
+# REQUIRES: x86
+
+# RUN: llvm-mc -triple=x86_64-win32 %s -filetype=obj -o %t.main.obj
+# RUN: llvm-mc -triple=x86_64-win32 %p/Inputs/otherFunc.s -filetype=obj -o %t.other.obj
+# RUN: llvm-ar rcs %t.other.lib %t.other.obj
+# RUN: not lld-link -out:%t.exe -entry:main %t.main.obj %p/Inputs/std64.lib %t.other.lib -opt:noref 2>&1 | FileCheck %s
+# CHECK: duplicate symbol: MessageBoxA
+
+.global main
+.text
+main:
+  callq MessageBoxA
+  callq ExitProcess
+  callq otherFunc
+  ret