diff --git a/src/library.js b/src/library.js
index d9e1942fa..d24f1f755 100644
--- a/src/library.js
+++ b/src/library.js
@@ -52,32 +52,33 @@ LibraryManager.library = {
       ___setErrNo(ERRNO_CODES.ENOTDIR);
       return 0;
     }
-    var err = _open(dirname, {{{ cDefine('O_RDONLY') }}}, allocate([0, 0, 0, 0], 'i32', ALLOC_STACK));
-    // open returns 0 on failure, not -1
-    return err === -1 ? 0 : err;
+    var fd = _open(dirname, {{{ cDefine('O_RDONLY') }}}, allocate([0, 0, 0, 0], 'i32', ALLOC_STACK));
+    return fd === -1 ? 0 : FS.getPtrForStream(FS.getStream(fd));
   },
-  closedir__deps: ['$FS', '__setErrNo', '$ERRNO_CODES', 'close'],
+  closedir__deps: ['$FS', '__setErrNo', '$ERRNO_CODES', 'close', 'fileno'],
   closedir: function(dirp) {
     // int closedir(DIR *dirp);
     // http://pubs.opengroup.org/onlinepubs/007908799/xsh/closedir.html
-    return _close(dirp);
+    var fd = _fileno(dirp);
+    return _close(fd);
   },
   telldir__deps: ['$FS', '__setErrNo', '$ERRNO_CODES'],
   telldir: function(dirp) {
     // long int telldir(DIR *dirp);
     // http://pubs.opengroup.org/onlinepubs/007908799/xsh/telldir.html
-    var stream = FS.getStream(dirp);
+    var stream = FS.getStreamFromPtr(dirp);
     if (!stream || !FS.isDir(stream.node.mode)) {
       ___setErrNo(ERRNO_CODES.EBADF);
       return -1;
     }
     return stream.position;
   },
-  seekdir__deps: ['$FS', '__setErrNo', '$ERRNO_CODES', 'lseek'],
+  seekdir__deps: ['$FS', '__setErrNo', '$ERRNO_CODES', 'lseek', 'fileno'],
   seekdir: function(dirp, loc) {
     // void seekdir(DIR *dirp, long int loc);
     // http://pubs.opengroup.org/onlinepubs/007908799/xsh/seekdir.html
-    _lseek(dirp, loc, {{{ cDefine('SEEK_SET') }}});
+    var fd = _fileno(dirp);
+    _lseek(fd, loc, {{{ cDefine('SEEK_SET') }}});
   },
   rewinddir__deps: ['seekdir'],
   rewinddir: function(dirp) {
@@ -89,7 +90,7 @@ LibraryManager.library = {
   readdir_r: function(dirp, entry, result) {
     // int readdir_r(DIR *dirp, struct dirent *entry, struct dirent **result);
     // http://pubs.opengroup.org/onlinepubs/007908799/xsh/readdir_r.html
-    var stream = FS.getStream(dirp);
+    var stream = FS.getStreamFromPtr(dirp);
     if (!stream) {
       return ___setErrNo(ERRNO_CODES.EBADF);
     }
@@ -134,7 +135,7 @@ LibraryManager.library = {
   readdir: function(dirp) {
     // struct dirent *readdir(DIR *dirp);
     // http://pubs.opengroup.org/onlinepubs/007908799/xsh/readdir_r.html
-    var stream = FS.getStream(dirp);
+    var stream = FS.getStreamFromPtr(dirp);
     if (!stream) {
       ___setErrNo(ERRNO_CODES.EBADF);
       return 0;
@@ -2290,19 +2291,20 @@ LibraryManager.library = {
   clearerr: function(stream) {
     // void clearerr(FILE *stream);
     // http://pubs.opengroup.org/onlinepubs/000095399/functions/clearerr.html
-    stream = FS.getStream(stream);
+    stream = FS.getStreamFromPtr(stream);
     if (!stream) {
       return;
     }
     stream.eof = false;
     stream.error = false;
   },
-  fclose__deps: ['close', 'fsync'],
+  fclose__deps: ['close', 'fsync', 'fileno'],
   fclose: function(stream) {
     // int fclose(FILE *stream);
     // http://pubs.opengroup.org/onlinepubs/000095399/functions/fclose.html
-    _fsync(stream);
-    return _close(stream);
+    var fd = _fileno(stream);
+    _fsync(fd);
+    return _close(fd);
   },
   fdopen__deps: ['$FS', '__setErrNo', '$ERRNO_CODES'],
   fdopen: function(fildes, mode) {
@@ -2323,21 +2325,21 @@ LibraryManager.library = {
     } else {
       stream.error = false;
       stream.eof = false;
-      return fildes;
+      return FS.getPtrForStream(stream);
     }
   },
   feof__deps: ['$FS'],
   feof: function(stream) {
     // int feof(FILE *stream);
     // http://pubs.opengroup.org/onlinepubs/000095399/functions/feof.html
-    stream = FS.getStream(stream);
+    stream = FS.getStreamFromPtr(stream);
     return Number(stream && stream.eof);
   },
   ferror__deps: ['$FS'],
   ferror: function(stream) {
     // int ferror(FILE *stream);
     // http://pubs.opengroup.org/onlinepubs/000095399/functions/ferror.html
-    stream = FS.getStream(stream);
+    stream = FS.getStreamFromPtr(stream);
     return Number(stream && stream.error);
   },
   fflush__deps: ['$FS', '__setErrNo', '$ERRNO_CODES'],
@@ -2351,7 +2353,7 @@ LibraryManager.library = {
   fgetc: function(stream) {
     // int fgetc(FILE *stream);
     // http://pubs.opengroup.org/onlinepubs/000095399/functions/fgetc.html
-    var streamObj = FS.getStream(stream);
+    var streamObj = FS.getStreamFromPtr(stream);
     if (!streamObj) return -1;
     if (streamObj.eof || streamObj.error) return -1;
     var ret = _fread(_fgetc.ret, 1, 1, stream);
@@ -2376,7 +2378,7 @@ LibraryManager.library = {
   fgetpos: function(stream, pos) {
     // int fgetpos(FILE *restrict stream, fpos_t *restrict pos);
     // http://pubs.opengroup.org/onlinepubs/000095399/functions/fgetpos.html
-    stream = FS.getStream(stream);
+    stream = FS.getStreamFromPtr(stream);
     if (!stream) {
       ___setErrNo(ERRNO_CODES.EBADF);
       return -1;
@@ -2394,7 +2396,7 @@ LibraryManager.library = {
   fgets: function(s, n, stream) {
     // char *fgets(char *restrict s, int n, FILE *restrict stream);
     // http://pubs.opengroup.org/onlinepubs/000095399/functions/fgets.html
-    var streamObj = FS.getStream(stream);
+    var streamObj = FS.getStreamFromPtr(stream);
     if (!streamObj) return 0;
     if (streamObj.error || streamObj.eof) return 0;
     var byte_;
@@ -2418,8 +2420,7 @@ LibraryManager.library = {
   fileno: function(stream) {
     // int fileno(FILE *stream);
     // http://pubs.opengroup.org/onlinepubs/000095399/functions/fileno.html
-    // We use file descriptor numbers and FILE* streams interchangeably.
-    return stream;
+    return FS.getStreamFromPtr(stream).fd;
   },
   ftrylockfile: function() {
     // int ftrylockfile(FILE *file);
@@ -2461,19 +2462,20 @@ LibraryManager.library = {
       ___setErrNo(ERRNO_CODES.EINVAL);
       return 0;
     }
-    var ret = _open(filename, flags, allocate([0x1FF, 0, 0, 0], 'i32', ALLOC_STACK));  // All creation permissions.
-    return (ret == -1) ? 0 : ret;
+    var fd = _open(filename, flags, allocate([0x1FF, 0, 0, 0], 'i32', ALLOC_STACK));  // All creation permissions.
+    return fd === -1 ? 0 : FS.getPtrForStream(FS.getStream(fd));
   },
-  fputc__deps: ['$FS', 'write'],
+  fputc__deps: ['$FS', 'write', 'fileno'],
   fputc__postset: '_fputc.ret = allocate([0], "i8", ALLOC_STATIC);',
   fputc: function(c, stream) {
     // int fputc(int c, FILE *stream);
     // http://pubs.opengroup.org/onlinepubs/000095399/functions/fputc.html
     var chr = unSign(c & 0xFF);
     {{{ makeSetValue('_fputc.ret', '0', 'chr', 'i8') }}};
-    var ret = _write(stream, _fputc.ret, 1);
+    var fd = _fileno(stream);
+    var ret = _write(fd, _fputc.ret, 1);
     if (ret == -1) {
-      var streamObj = FS.getStream(stream);
+      var streamObj = FS.getStreamFromPtr(stream);
       if (streamObj) streamObj.error = true;
       return -1;
     } else {
@@ -2489,11 +2491,12 @@ LibraryManager.library = {
     return _fputc(c, {{{ makeGetValue(makeGlobalUse('_stdout'), '0', 'void*') }}});
   },
   putchar_unlocked: 'putchar',
-  fputs__deps: ['write', 'strlen'],
+  fputs__deps: ['write', 'strlen', 'fileno'],
   fputs: function(s, stream) {
     // int fputs(const char *restrict s, FILE *restrict stream);
     // http://pubs.opengroup.org/onlinepubs/000095399/functions/fputs.html
-    return _write(stream, s, _strlen(s));
+    var fd = _fileno(stream);
+    return _write(fd, s, _strlen(s));
   },
   puts__deps: ['fputs', 'fputc', 'stdout'],
   puts: function(s) {
@@ -2518,7 +2521,7 @@ LibraryManager.library = {
       return 0;
     }
     var bytesRead = 0;
-    var streamObj = FS.getStream(stream);
+    var streamObj = FS.getStreamFromPtr(stream);
     if (!streamObj) {
       ___setErrNo(ERRNO_CODES.EBADF);
       return 0;
@@ -2528,7 +2531,7 @@ LibraryManager.library = {
       bytesToRead--;
       bytesRead++;
     }
-    var err = _read(stream, ptr, bytesToRead);
+    var err = _read(streamObj.fd, ptr, bytesToRead);
     if (err == -1) {
       if (streamObj) streamObj.error = true;
       return 0;
@@ -2542,7 +2545,7 @@ LibraryManager.library = {
     // FILE *freopen(const char *restrict filename, const char *restrict mode, FILE *restrict stream);
     // http://pubs.opengroup.org/onlinepubs/000095399/functions/freopen.html
     if (!filename) {
-      var streamObj = FS.getStream(stream);
+      var streamObj = FS.getStreamFromPtr(stream);
       if (!streamObj) {
         ___setErrNo(ERRNO_CODES.EBADF);
         return 0;
@@ -2554,15 +2557,16 @@ LibraryManager.library = {
     _fclose(stream);
     return _fopen(filename, mode);
   },
-  fseek__deps: ['$FS', 'lseek'],
+  fseek__deps: ['$FS', 'lseek', 'fileno'],
   fseek: function(stream, offset, whence) {
     // int fseek(FILE *stream, long offset, int whence);
     // http://pubs.opengroup.org/onlinepubs/000095399/functions/fseek.html
-    var ret = _lseek(stream, offset, whence);
+    var fd = _fileno(stream);
+    var ret = _lseek(fd, offset, whence);
     if (ret == -1) {
       return -1;
     }
-    stream = FS.getStream(stream);
+    stream = FS.getStreamFromPtr(stream);
     stream.eof = false;
     return 0;
   },
@@ -2571,7 +2575,7 @@ LibraryManager.library = {
   fsetpos: function(stream, pos) {
     // int fsetpos(FILE *stream, const fpos_t *pos);
     // http://pubs.opengroup.org/onlinepubs/000095399/functions/fsetpos.html
-    stream = FS.getStream(stream);
+    stream = FS.getStreamFromPtr(stream);
     if (!stream) {
       ___setErrNo(ERRNO_CODES.EBADF);
       return -1;
@@ -2590,7 +2594,7 @@ LibraryManager.library = {
   ftell: function(stream) {
     // long ftell(FILE *stream);
     // http://pubs.opengroup.org/onlinepubs/000095399/functions/ftell.html
-    stream = FS.getStream(stream);
+    stream = FS.getStreamFromPtr(stream);
     if (!stream) {
       ___setErrNo(ERRNO_CODES.EBADF);
       return -1;
@@ -2603,15 +2607,16 @@ LibraryManager.library = {
     }
   },
   ftello: 'ftell',
-  fwrite__deps: ['$FS', 'write'],
+  fwrite__deps: ['$FS', 'write', 'fileno'],
   fwrite: function(ptr, size, nitems, stream) {
     // size_t fwrite(const void *restrict ptr, size_t size, size_t nitems, FILE *restrict stream);
     // http://pubs.opengroup.org/onlinepubs/000095399/functions/fwrite.html
     var bytesToWrite = nitems * size;
     if (bytesToWrite == 0) return 0;
-    var bytesWritten = _write(stream, ptr, bytesToWrite);
+    var fd = _fileno(stream);
+    var bytesWritten = _write(fd, ptr, bytesToWrite);
     if (bytesWritten == -1) {
-      var streamObj = FS.getStream(stream);
+      var streamObj = FS.getStreamFromPtr(stream);
       if (streamObj) streamObj.error = true;
       return 0;
     } else {
@@ -2674,7 +2679,7 @@ LibraryManager.library = {
     // void rewind(FILE *stream);
     // http://pubs.opengroup.org/onlinepubs/000095399/functions/rewind.html
     _fseek(stream, 0, 0);  // SEEK_SET.
-    var streamObj = FS.getStream(stream);
+    var streamObj = FS.getStreamFromPtr(stream);
     if (streamObj) streamObj.error = false;
   },
   setvbuf: function(stream, buf, type, size) {
@@ -2731,7 +2736,7 @@ LibraryManager.library = {
   ungetc: function(c, stream) {
     // int ungetc(int c, FILE *stream);
     // http://pubs.opengroup.org/onlinepubs/000095399/functions/ungetc.html
-    stream = FS.getStream(stream);
+    stream = FS.getStreamFromPtr(stream);
     if (!stream) {
       return -1;
     }
@@ -2756,7 +2761,7 @@ LibraryManager.library = {
   fscanf: function(stream, format, varargs) {
     // int fscanf(FILE *restrict stream, const char *restrict format, ... );
     // http://pubs.opengroup.org/onlinepubs/000095399/functions/scanf.html
-    var streamObj = FS.getStream(stream);
+    var streamObj = FS.getStreamFromPtr(stream);
     if (!streamObj) {
       return -1;
     }
@@ -2899,7 +2904,7 @@ LibraryManager.library = {
   // ==========================================================================
 
   mmap__deps: ['$FS'],
-  mmap: function(start, num, prot, flags, stream, offset) {
+  mmap: function(start, num, prot, flags, fd, offset) {
     /* FIXME: Since mmap is normally implemented at the kernel level,
      * this implementation simply uses malloc underneath the call to
      * mmap.
@@ -2910,13 +2915,13 @@ LibraryManager.library = {
 
     if (!_mmap.mappings) _mmap.mappings = {};
 
-    if (stream == -1) {
+    if (fd == -1) {
       ptr = _malloc(num);
       if (!ptr) return -1;
       _memset(ptr, 0, num);
       allocated = true;
     } else {
-      var info = FS.getStream(stream);
+      var info = FS.getStream(fd);
       if (!info) return -1;
       try {
         var res = FS.mmap(info, HEAPU8, start, num, offset, prot, flags);
diff --git a/src/library_fs.js b/src/library_fs.js
index 8d83048e3..e97ba588d 100644
--- a/src/library_fs.js
+++ b/src/library_fs.js
@@ -413,6 +413,22 @@ mergeInto(LibraryManager.library, {
       FS.streams[fd] = null;
     },
 
+    //
+    // file pointers
+    //
+    // instead of maintaining a separate mapping from FILE* to file descriptors,
+    // we employ a simple trick: the pointer to a stream is its fd plus 1.  This
+    // means that all valid streams have a valid non-zero pointer while allowing
+    // the fs for stdin to be the standard value of zero.
+    // 
+    //
+    getStreamFromPtr: function(ptr) {
+      return FS.streams[ptr - 1];
+    },
+    getPtrForStream: function(stream) {
+      return stream ? stream.fd + 1 : 0;
+    },
+
     //
     // devices
     //
@@ -1166,15 +1182,15 @@ mergeInto(LibraryManager.library, {
 
       // open default streams for the stdin, stdout and stderr devices
       var stdin = FS.open('/dev/stdin', 'r');
-      {{{ makeSetValue(makeGlobalUse('_stdin'), 0, 'stdin.fd', 'void*') }}};
+      {{{ makeSetValue(makeGlobalUse('_stdin'), 0, 'FS.getPtrForStream(stdin)', 'void*') }}};
       assert(stdin.fd === 0, 'invalid handle for stdin (' + stdin.fd + ')');
 
       var stdout = FS.open('/dev/stdout', 'w');
-      {{{ makeSetValue(makeGlobalUse('_stdout'), 0, 'stdout.fd', 'void*') }}};
+      {{{ makeSetValue(makeGlobalUse('_stdout'), 0, 'FS.getPtrForStream(stdout)', 'void*') }}};
       assert(stdout.fd === 1, 'invalid handle for stdout (' + stdout.fd + ')');
 
       var stderr = FS.open('/dev/stderr', 'w');
-      {{{ makeSetValue(makeGlobalUse('_stderr'), 0, 'stderr.fd', 'void*') }}};
+      {{{ makeSetValue(makeGlobalUse('_stderr'), 0, 'FS.getPtrForStream(stderr)', 'void*') }}};
       assert(stderr.fd === 2, 'invalid handle for stderr (' + stderr.fd + ')');
     },
     ensureErrnoError: function() {