Index: include/llvm/MC/MCObjectWriter.h
===================================================================
--- include/llvm/MC/MCObjectWriter.h
+++ include/llvm/MC/MCObjectWriter.h
@@ -49,6 +49,10 @@
   MCObjectWriter(raw_pwrite_stream &OS, bool IsLittleEndian)
       : OS(&OS), IsLittleEndian(IsLittleEndian) {}
 
+  unsigned getInitialOffset() {
+    return OS->tell();
+  }
+
 public:
   virtual ~MCObjectWriter();
 
Index: lib/MC/WinCOFFObjectWriter.cpp
===================================================================
--- lib/MC/WinCOFFObjectWriter.cpp
+++ lib/MC/WinCOFFObjectWriter.cpp
@@ -962,7 +962,7 @@
 
   // Assign file offsets to COFF object file structures.
 
-  unsigned offset = 0;
+  unsigned offset = getInitialOffset();
 
   if (UseBigObj)
     offset += COFF::Header32Size;
Index: test/MC/COFF/stdin.s
===================================================================
--- /dev/null
+++ test/MC/COFF/stdin.s
@@ -0,0 +1,3 @@
+// REQUIRES: shell
+// RUN: ( echo "test"; llvm-mc -filetype=obj -triple i686-pc-win32 %s ) > %t
+