diff --git a/include/llvm/System/MappedFile.h b/include/llvm/System/MappedFile.h
index c46491ee7da..127c04f002d 100644
--- a/include/llvm/System/MappedFile.h
+++ b/include/llvm/System/MappedFile.h
@@ -65,15 +65,13 @@ namespace sys {
       return initialize(ErrMsg);
     }
 
-    /// unmap - Remove the mapped file from memory. If the file was mapped for
-    /// write access, the memory contents will be automatically synchronized
-    /// with the file's disk contents.
+    /// unmap - Remove the mapped file from memory.
     void unmap();
 
     /// map - Reserve space for the file, map it into memory, and return a
     /// pointer to it.  This returns the base memory address of the mapped file
     /// or 0 if an error occurred.
-    void *map(std::string* ErrMsg = 0);
+    const void *map(std::string* ErrMsg = 0);
 
     void close() { if (MapInfo) terminate(); }
 
diff --git a/lib/System/Unix/MappedFile.inc b/lib/System/Unix/MappedFile.inc
index 92dc6660439..35efaa6fcb9 100644
--- a/lib/System/Unix/MappedFile.inc
+++ b/lib/System/Unix/MappedFile.inc
@@ -56,6 +56,7 @@ bool MappedFile::initialize(std::string* ErrMsg) {
 }
 
 void MappedFile::terminate() {
+  unmap();
   assert(MapInfo && "MappedFile not initialized");
   ::close(MapInfo->FD);
   delete MapInfo;
@@ -70,7 +71,7 @@ void MappedFile::unmap() {
   BasePtr = 0;  // Mark this as non-mapped.
 }
 
-void* MappedFile::map(std::string* ErrMsg) {
+const void* MappedFile::map(std::string* ErrMsg) {
   assert(MapInfo && "MappedFile not initialized");
   if (isMapped()) return BasePtr;
   
diff --git a/lib/System/Win32/MappedFile.inc b/lib/System/Win32/MappedFile.inc
index 830905debca..4f30f56f74c 100644
--- a/lib/System/Win32/MappedFile.inc
+++ b/lib/System/Win32/MappedFile.inc
@@ -75,7 +75,7 @@ void MappedFile::unmap() {
   }
 }
 
-void* MappedFile::map(std::string* ErrMsg) {
+const void* MappedFile::map(std::string* ErrMsg) {
   if (!isMapped()) {
     MapInfo->hMapping = CreateFileMapping(MapInfo->hFile, NULL, PAGE_READONLY,
                                           0, 0, NULL);