Index: COFF/Config.h
===================================================================
--- COFF/Config.h
+++ COFF/Config.h
@@ -94,7 +94,8 @@
   bool DoICF = true;
   bool TailMerge;
   bool Relocatable = true;
-  bool Force = false;
+  bool ForceMultiple = false;
+  bool ForceUnresolved = false;
   bool Debug = false;
   bool DebugDwarf = false;
   bool DebugGHashes = false;
Index: COFF/Driver.cpp
===================================================================
--- COFF/Driver.cpp
+++ COFF/Driver.cpp
@@ -837,8 +837,12 @@
 
   // Handle /force or /force:unresolved
   if (Args.hasArg(OPT_force, OPT_force_unresolved))
-    Config->Force = true;
+    Config->ForceUnresolved = true;
 
+  // Handle /force or /force:multiple
+  if (Args.hasArg(OPT_force, OPT_force_multiple))
+    Config->ForceMultiple = true;
+  
   // Handle /debug
   if (Args.hasArg(OPT_debug, OPT_debug_dwarf, OPT_debug_ghash)) {
     Config->Debug = true;
Index: COFF/Options.td
===================================================================
--- COFF/Options.td
+++ COFF/Options.td
@@ -99,8 +99,11 @@
 def wholearchive_flag : F<"wholearchive">;
 
 def force : F<"force">,
+    HelpText<"Allow undefined and multiply defined symbols when creating executables">;
+def force_unresolved : F<"force:unresolved">, 
     HelpText<"Allow undefined symbols when creating executables">;
-def force_unresolved : F<"force:unresolved">;
+def force_multiple : F<"force:multiple">, 
+    HelpText<"Allow multiply defined symbols when creating executables">;
 defm WX : B<"WX", "Treat warnings as errors", "Don't treat warnings as errors">;
 
 defm allowbind : B<"allowbind", "Enable DLL binding (default)",
Index: COFF/SymbolTable.cpp
===================================================================
--- COFF/SymbolTable.cpp
+++ COFF/SymbolTable.cpp
@@ -59,8 +59,15 @@
   Driver->parseDirectives(S);
 }
 
-static void errorOrWarn(const Twine &S) {
-  if (Config->Force)
+static void errorOrWarnMultiple(const Twine &S) {
+  if (Config->ForceMultiple)
+    warn(S);
+  else
+    error(S);
+}
+
+static void errorOrWarnUnresolved(const Twine &S) {
+  if (Config->ForceUnresolved)
     warn(S);
   else
     error(S);
@@ -171,7 +178,7 @@
 
     // Remaining undefined symbols are not fatal if /force is specified.
     // They are replaced with dummy defined symbols.
-    if (Config->Force)
+    if (Config->ForceUnresolved)
       replaceSymbol<DefinedAbsolute>(Sym, Name, 0);
     Undefs.insert(Sym);
   }
@@ -181,7 +188,7 @@
 
   for (Symbol *B : Config->GCRoot) {
     if (Undefs.count(B))
-      errorOrWarn("<root>: undefined symbol: " + B->getName());
+      errorOrWarnUnresolved("<root>: undefined symbol: " + B->getName());
     if (Config->WarnLocallyDefinedImported)
       if (Symbol *Imp = LocalImports.lookup(B))
         warn("<root>: locally defined symbol imported: " + Imp->getName() +
@@ -195,7 +202,7 @@
       if (!Sym)
         continue;
       if (Undefs.count(Sym))
-        errorOrWarn("undefined symbol: " + Sym->getName() +
+        errorOrWarnUnresolved("undefined symbol: " + Sym->getName() +
                     getSymbolLocations(File, SymIndex));
       if (Config->WarnLocallyDefinedImported)
         if (Symbol *Imp = LocalImports.lookup(Sym))
@@ -255,8 +262,8 @@
 }
 
 void SymbolTable::reportDuplicate(Symbol *Existing, InputFile *NewFile) {
-  error("duplicate symbol: " + toString(*Existing) + " in " +
-        toString(Existing->getFile()) + " and in " + toString(NewFile));
+  errorOrWarnMultiple("duplicate symbol: " + toString(*Existing) + " in " +
+          toString(Existing->getFile()) + " and in " + toString(NewFile));
 }
 
 Symbol *SymbolTable::addAbsolute(StringRef N, COFFSymbolRef Sym) {