Index: lld/trunk/COFF/SymbolTable.cpp
===================================================================
--- lld/trunk/COFF/SymbolTable.cpp
+++ lld/trunk/COFF/SymbolTable.cpp
@@ -177,7 +177,8 @@
     if (!Sym->Body.compare_exchange_strong(Existing, New))
       continue;
     New->setBackref(Sym);
-    Accum->push_back(Sym);
+    if (isa<Undefined>(Existing))
+      Accum->push_back(Sym);
     return;
   }
 }
Index: lld/trunk/test/COFF/ar-comdat.test
===================================================================
--- lld/trunk/test/COFF/ar-comdat.test
+++ lld/trunk/test/COFF/ar-comdat.test
@@ -0,0 +1,38 @@
+# RUN: yaml2obj %s > %t1.obj
+# RUN: yaml2obj %s > %t2.obj
+# RUN: llvm-lib /out:%t.lib %t1.obj %t2.obj
+# RUN: lld -flavor link2 /out:%t.exe /lldmap:%t.map /entry:main /subsystem:console %p/Inputs/ret42.obj %t.lib
+# RUN: FileCheck %s < %t.map
+
+# CHECK-NOT: .lib
+
+---
+header:          
+  Machine:         IMAGE_FILE_MACHINE_AMD64
+  Characteristics: [  ]
+sections:        
+  - Name:            .bss
+    Characteristics: [ IMAGE_SCN_CNT_UNINITIALIZED_DATA, IMAGE_SCN_LNK_COMDAT, IMAGE_SCN_MEM_READ, IMAGE_SCN_MEM_WRITE ]
+    Alignment:       4
+    SectionData:     ''
+symbols:         
+  - Name:            .bss
+    Value:           0
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+    SectionDefinition: 
+      Length:          4
+      NumberOfRelocations: 0
+      NumberOfLinenumbers: 0
+      CheckSum:        0
+      Number:          1
+      Selection:       IMAGE_COMDAT_SELECT_ANY
+  - Name:            x
+    Value:           0
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+...