diff --git a/include/llvm/Support/MemoryBuffer.h b/include/llvm/Support/MemoryBuffer.h
index 8067216..d7e0317 100644
--- a/include/llvm/Support/MemoryBuffer.h
+++ b/include/llvm/Support/MemoryBuffer.h
@@ -15,6 +15,7 @@
 #define LLVM_SUPPORT_MEMORYBUFFER_H
 
 #include "llvm/Support/DataTypes.h"
+#include <string>
 
 namespace llvm {
 
@@ -52,6 +53,7 @@
   /// specified, this means that the client knows that the file exists and that
   /// it has the specified size.
   static MemoryBuffer *getFile(const char *FilenameStart, unsigned FnSize,
+                               std::string *ErrStr = 0,
                                int64_t FileSize = -1);
 
   /// getMemBuffer - Open the specified memory range as a MemoryBuffer.  Note
@@ -79,14 +81,24 @@
   
   
   /// getFileOrSTDIN - Open the specified file as a MemoryBuffer, or open stdin
-  /// if the Filename is "-".
+  /// if the Filename is "-".  If an error occurs, this returns null and fills
+  /// in *ErrStr with a reason.
   static MemoryBuffer *getFileOrSTDIN(const char *FilenameStart,unsigned FnSize,
+                                      std::string *ErrStr = 0,
                                       int64_t FileSize = -1) {
     if (FnSize == 1 && FilenameStart[0] == '-')
       return getSTDIN();
-    return getFile(FilenameStart, FnSize, FileSize);
+    return getFile(FilenameStart, FnSize, ErrStr, FileSize);
   }
   
+  /// getFileOrSTDIN - Open the specified file as a MemoryBuffer, or open stdin
+  /// if the Filename is "-".  If an error occurs, this returns null and fills
+  /// in *ErrStr with a reason.
+  static MemoryBuffer *getFileOrSTDIN(const std::string &FN,
+                                      std::string *ErrStr = 0,
+                                      int64_t FileSize = -1) {
+    return getFileOrSTDIN(&FN[0], FN.size(), ErrStr, FileSize);
+  }
 };
 
 } // end namespace llvm
diff --git a/lib/Support/MemoryBuffer.cpp b/lib/Support/MemoryBuffer.cpp
index ffbb4be..b2c561c 100644
--- a/lib/Support/MemoryBuffer.cpp
+++ b/lib/Support/MemoryBuffer.cpp
@@ -113,7 +113,7 @@
 public:
   MemoryBufferMMapFile() {}
   
-  bool open(const sys::Path &Filename);
+  bool open(const sys::Path &Filename, std::string *ErrStr);
   
   virtual const char *getBufferIdentifier() const {
     return File.path().c_str();
@@ -123,13 +123,15 @@
 };
 }
 
-bool MemoryBufferMMapFile::open(const sys::Path &Filename) {
+bool MemoryBufferMMapFile::open(const sys::Path &Filename,
+                                std::string *ErrStr) {
   // FIXME: This does an extra stat syscall to figure out the size, but we
   // already know the size!
-  bool Failure = File.open(Filename);
+  bool Failure = File.open(Filename, sys::MappedFile::READ_ACCESS, ErrStr);
   if (Failure) return true;
   
-  File.map();
+  if (!File.map(ErrStr))
+    return true;
   
   size_t Size = File.size();
   
@@ -161,11 +163,13 @@
 //===----------------------------------------------------------------------===//
 
 MemoryBuffer *MemoryBuffer::getFile(const char *FilenameStart, unsigned FnSize,
-                                    int64_t FileSize) {
+                                    std::string *ErrStr, int64_t FileSize){
+  // FIXME: it would be nice if PathWithStatus didn't copy the filename into a
+  // temporary string. :(
   sys::PathWithStatus P(FilenameStart, FnSize);
 #if 1
   MemoryBufferMMapFile *M = new MemoryBufferMMapFile();
-  if (!M->open(P))
+  if (!M->open(P, ErrStr))
     return M;
   delete M;
   return 0;
@@ -186,7 +190,7 @@
   // If the file is larger than some threshold, use mmap, otherwise use 'read'.
   if (FileSize >= 4096*4) {
     MemoryBufferMMapFile *M = new MemoryBufferMMapFile();
-    if (!M->open(P))
+    if (!M->open(P, ErrStr))
       return M;
     delete M;
     return 0;