Index: lib/Object/COFFModuleDefinition.cpp
===================================================================
--- lib/Object/COFFModuleDefinition.cpp
+++ lib/Object/COFFModuleDefinition.cpp
@@ -227,6 +227,10 @@
         E.Name = (std::string("_").append(E.Name));
       if (!E.ExtName.empty() && !isDecorated(E.ExtName, MingwDef))
         E.ExtName = (std::string("_").append(E.ExtName));
+      if (MingwDef) {
+        E.SymbolName = E.Name;
+        E.Name = E.Name.substr(0, E.Name.find('@'));
+      }
     }
 
     for (;;) {
Index: test/DllTool/coff-stdcall.def
===================================================================
--- /dev/null
+++ test/DllTool/coff-stdcall.def
@@ -0,0 +1,13 @@
+; RUN: llvm-dlltool -m i386 --input-def %s --output-lib %t.a
+; RUN: llvm-readobj %t.a | FileCheck %s
+
+LIBRARY test.dll
+EXPORTS
+TestFunction@4
+
+; CHECK: File: test.dll
+; CHECK: Format: COFF-import-file
+; CHECK: Type: code
+; CHECK: Name type: undecorate
+; CHECK: Symbol: __imp__TestFunction@4
+; CHECK: Symbol: _TestFunction@4