diff --git a/lld/COFF/InputFiles.cpp b/lld/COFF/InputFiles.cpp
--- a/lld/COFF/InputFiles.cpp
+++ b/lld/COFF/InputFiles.cpp
@@ -1070,7 +1070,8 @@
         sym = ctx.symtab.addUndefined(symName, this, false);
       }
     } else {
-      sym = ctx.symtab.addRegular(this, symName, nullptr, fakeSC);
+      sym = ctx.symtab.addRegular(this, symName, nullptr, fakeSC, 0,
+                                  objSym.isWeak());
     }
     symbols.push_back(sym);
     if (objSym.isUsed())
diff --git a/lld/COFF/SymbolTable.h b/lld/COFF/SymbolTable.h
--- a/lld/COFF/SymbolTable.h
+++ b/lld/COFF/SymbolTable.h
@@ -95,7 +95,8 @@
   Symbol *addAbsolute(StringRef n, COFFSymbolRef s);
   Symbol *addRegular(InputFile *f, StringRef n,
                      const llvm::object::coff_symbol_generic *s = nullptr,
-                     SectionChunk *c = nullptr, uint32_t sectionOffset = 0);
+                     SectionChunk *c = nullptr, uint32_t sectionOffset = 0,
+                     bool isWeak = false);
   std::pair<DefinedRegular *, bool>
   addComdat(InputFile *f, StringRef n,
             const llvm::object::coff_symbol_generic *s = nullptr);
diff --git a/lld/COFF/SymbolTable.cpp b/lld/COFF/SymbolTable.cpp
--- a/lld/COFF/SymbolTable.cpp
+++ b/lld/COFF/SymbolTable.cpp
@@ -698,12 +698,12 @@
 
 Symbol *SymbolTable::addRegular(InputFile *f, StringRef n,
                                 const coff_symbol_generic *sym, SectionChunk *c,
-                                uint32_t sectionOffset) {
+                                uint32_t sectionOffset, bool isWeak) {
   auto [s, wasInserted] = insert(n, f);
-  if (wasInserted || !isa<DefinedRegular>(s))
+  if (wasInserted || !isa<DefinedRegular>(s) || s->isWeak)
     replaceSymbol<DefinedRegular>(s, f, n, /*IsCOMDAT*/ false,
-                                  /*IsExternal*/ true, sym, c);
-  else
+                                  /*IsExternal*/ true, sym, c, isWeak);
+  else if (!isWeak)
     reportDuplicate(s, f, c, sectionOffset);
   return s;
 }
diff --git a/lld/COFF/Symbols.h b/lld/COFF/Symbols.h
--- a/lld/COFF/Symbols.h
+++ b/lld/COFF/Symbols.h
@@ -106,7 +106,8 @@
       : symbolKind(k), isExternal(true), isCOMDAT(false),
         writtenToSymtab(false), pendingArchiveLoad(false), isGCRoot(false),
         isRuntimePseudoReloc(false), deferUndefined(false), canInline(true),
-        nameSize(n.size()), nameData(n.empty() ? nullptr : n.data()) {
+        isWeak(false), nameSize(n.size()),
+        nameData(n.empty() ? nullptr : n.data()) {
     assert((!n.empty() || k <= LastDefinedCOFFKind) &&
            "If the name is empty, the Symbol must be a DefinedCOFF.");
   }
@@ -145,6 +146,11 @@
   // doesn't know the final contents of the symbol.
   unsigned canInline : 1;
 
+  // True if the symbol is weak. This is only tracked for bitcode/LTO symbols.
+  // This information isn't written to the output; rather, it's used for
+  // managing weak symbol overrides.
+  unsigned isWeak : 1;
+
 protected:
   // Symbol name length. Assume symbol lengths fit in a 32-bit integer.
   uint32_t nameSize;
@@ -200,10 +206,11 @@
   DefinedRegular(InputFile *f, StringRef n, bool isCOMDAT,
                  bool isExternal = false,
                  const coff_symbol_generic *s = nullptr,
-                 SectionChunk *c = nullptr)
+                 SectionChunk *c = nullptr, bool isWeak = false)
       : DefinedCOFF(DefinedRegularKind, f, n, s), data(c ? &c->repl : nullptr) {
     this->isExternal = isExternal;
     this->isCOMDAT = isCOMDAT;
+    this->isWeak = isWeak;
   }
 
   static bool classof(const Symbol *s) {
diff --git a/lld/test/COFF/Inputs/strong-def.ll b/lld/test/COFF/Inputs/strong-def.ll
new file mode 100644
--- /dev/null
+++ b/lld/test/COFF/Inputs/strong-def.ll
@@ -0,0 +1,6 @@
+target datalayout = "e-m:w-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-windows-msvc"
+
+define dso_local noundef i32 @foo() local_unnamed_addr {
+  ret i32 5678
+}
diff --git a/lld/test/COFF/Inputs/weak-def.ll b/lld/test/COFF/Inputs/weak-def.ll
new file mode 100644
--- /dev/null
+++ b/lld/test/COFF/Inputs/weak-def.ll
@@ -0,0 +1,6 @@
+target datalayout = "e-m:w-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-windows-msvc"
+
+define weak dso_local noundef i32 @foo() local_unnamed_addr {
+  ret i32 1234
+}
diff --git a/lld/test/COFF/weak-override.ll b/lld/test/COFF/weak-override.ll
new file mode 100644
--- /dev/null
+++ b/lld/test/COFF/weak-override.ll
@@ -0,0 +1,30 @@
+; REQUIRES: x86
+; RUN: llvm-as -o %t-weak.obj %S/Inputs/weak-def.ll
+; RUN: llvm-as -o %t-strong.obj %S/Inputs/strong-def.ll
+; RUN: llvm-as -o %t.obj %s
+; RUN: lld-link /dll /out:%t-weak-first.dll %t.obj %t-weak.obj %t-strong.obj
+; RUN: lld-link /dll /out:%t-strong-first.dll %t.obj %t-strong.obj %t-weak.obj
+; RUN: lld-link /dll /out:%t-weak-only.dll %t.obj %t-weak.obj
+; RUN: llvm-objdump -d %t-weak-first.dll | FileCheck --check-prefix=CHECK-STRONG %s
+; RUN: llvm-objdump -d %t-strong-first.dll | FileCheck --check-prefix=CHECK-STRONG %s
+; RUN: llvm-objdump -d %t-weak-only.dll | FileCheck --check-prefix=CHECK-WEAK %s
+
+target datalayout = "e-m:w-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-windows-msvc"
+
+declare noundef i32 @foo() local_unnamed_addr
+
+define dllexport i32 @bar() local_unnamed_addr {
+  %1 = tail call noundef i32 @foo()
+  ret i32 %1
+}
+
+define void @_DllMainCRTStartup() {
+entry:
+  ret void
+}
+
+; CHECK-STRONG: movl $5678, %eax
+; CHECK-STRONG-NOT: movl $1234, %eax
+; CHECK-WEAK: movl $1234, %eax
+; CHECK-WEAK-NOT: movl $5678, %eax