diff --git a/db/db.cpp b/db/db.cpp
index db9e3914114..5a3677c5653 100644
--- a/db/db.cpp
+++ b/db/db.cpp
@@ -72,7 +72,8 @@ namespace mongo {
         out() << "quicktest()\n";
 
         MemoryMappedFile mmf;
-        char *m = (char *) mmf.map("/tmp/quicktest", 16384);
+        int len = 16384;
+        char *m = (char *) mmf.map("/tmp/quicktest", len);
         //	out() << "mmf reads: " << m << endl;
         strcpy_s(m, 1000, "hello worldz");
     }
diff --git a/db/namespace.cpp b/db/namespace.cpp
index e97139f1428..0cde591bf6d 100644
--- a/db/namespace.cpp
+++ b/db/namespace.cpp
@@ -63,7 +63,7 @@ namespace mongo {
             i.dbDropped();
         }
 
-        const int LEN = 16 * 1024 * 1024;
+        int LEN = 16 * 1024 * 1024;
         string pathString = path().string();
         void *p = f.map(pathString.c_str(), LEN);
         if ( p == 0 ) {
diff --git a/db/pdfile.cpp b/db/pdfile.cpp
index bdf40b62094..e4ec701290c 100644
--- a/db/pdfile.cpp
+++ b/db/pdfile.cpp
@@ -248,7 +248,6 @@ namespace mongo {
             uassert("can't map file memory - mongo requires 64 bit build for larger datasets", header);
         else
             uassert("can't map file memory", header);
-        // If opening an existing file, this is a no-op.
         header->init(fileNo, size);
     }
 
diff --git a/db/tests.cpp b/db/tests.cpp
index 85804daa499..760535e816a 100644
--- a/db/tests.cpp
+++ b/db/tests.cpp
@@ -32,7 +32,8 @@ namespace mongo {
 
         MemoryMappedFile f;
 
-        char *p = (char *) f.map("/tmp/test.dat", 64*1024*1024);
+        int len = 64*1024*1024;
+        char *p = (char *) f.map("/tmp/test.dat", len);
         char *start = p;
         char *end = p + 64*1024*1024-2;
         end[1] = 'z';
diff --git a/util/file_allocator.h b/util/file_allocator.h
index f043b32ef97..f70a1547bfb 100644
--- a/util/file_allocator.h
+++ b/util/file_allocator.h
@@ -51,7 +51,7 @@ namespace mongo {
         }
         // Returns when file has been allocated.  If file exists, size is
         // updated to match existing file size.
-        void allocateAsap( const string &name, int size ) {
+        void allocateAsap( const string &name, int &size ) {
             {
                 boostlock lk( pendingMutex_ );
                 int oldSize = prevSize( name );
diff --git a/util/mmap.cpp b/util/mmap.cpp
index a68cff77fc2..6b2ee813c33 100644
--- a/util/mmap.cpp
+++ b/util/mmap.cpp
@@ -58,7 +58,8 @@ namespace mongo {
     void* MemoryMappedFile::map(const char *filename) {
         boost::uintmax_t l = boost::filesystem::file_size( filename );
         assert( l <= 0x7fffffff );
-        return map( filename , (int) l );
+        int i = l;
+        return map( filename , i );
     }
 
 } // namespace mongo
diff --git a/util/mmap.h b/util/mmap.h
index 110f041039e..55ae7a7bf37 100644
--- a/util/mmap.h
+++ b/util/mmap.h
@@ -30,9 +30,10 @@ namespace mongo {
         // Throws exception if file doesn't exist.
         void* map( const char *filename );
 
-        /* Creates with length if DNE, otherwise uses existing file length.
+        /* Creates with length if DNE, otherwise uses existing file length,
+           passed length.
         */
-        void* map(const char *filename, int length);
+        void* map(const char *filename, int &length);
 
         void flush(bool sync);
 
diff --git a/util/mmap_posix.cpp b/util/mmap_posix.cpp
index aacf993e6f1..5cd83a8021d 100644
--- a/util/mmap_posix.cpp
+++ b/util/mmap_posix.cpp
@@ -50,7 +50,7 @@ namespace mongo {
 #define O_NOATIME 0
 #endif
 
-    void* MemoryMappedFile::map(const char *filename, int length) {
+    void* MemoryMappedFile::map(const char *filename, int &length) {
         // length may be updated by callee.
         theFileAllocator().allocateAsap( filename, length );
         len = length;
diff --git a/util/mmap_win.cpp b/util/mmap_win.cpp
index f0d799ad73d..8828263159f 100644
--- a/util/mmap_win.cpp
+++ b/util/mmap_win.cpp
@@ -49,7 +49,7 @@ namespace mongo {
 
     unsigned mapped = 0;
 
-    void* MemoryMappedFile::map(const char *_filename, int length) {
+    void* MemoryMappedFile::map(const char *_filename, int &length) {
         /* big hack here: Babble uses db names with colons.  doesn't seem to work on windows.  temporary perhaps. */
         char filename[256];
         strncpy(filename, _filename, 255);