diff --git a/doc/notes.txt b/doc/notes.txt
index fba114c5..d9dc6d53 100644
--- a/doc/notes.txt
+++ b/doc/notes.txt
@@ -53,6 +53,8 @@ TODO:
 - how to revert included files?
 - go to error in include files
 - BOM in upload/download?
+- don't mess with localStorage when migrating!
+
 
 WEB WORKER FORMAT
 
diff --git a/src/store.ts b/src/store.ts
index a89f0071..7406c2cc 100644
--- a/src/store.ts
+++ b/src/store.ts
@@ -112,7 +112,7 @@ function copyFromOldStorageFormat(platformid:string, newstore, callback:()=>void
 
 function createNewPersistentStore(platformid:string, callback:()=>void) {
   var store = localforage.createInstance({
-    name: platformid,
+    name: "__" + platformid,
     version: 2.0
   });
   copyFromOldStorageFormat(platformid, store, callback);
diff --git a/src/worker/workermain.js b/src/worker/workermain.js
index 413dc2bf..afa9911b 100644
--- a/src/worker/workermain.js
+++ b/src/worker/workermain.js
@@ -337,10 +337,29 @@ function loadNative(modulename, debug) {
 
 // mount the filesystem at /share
 function setupFS(FS, name) {
+  var WORKERFS = FS.filesystems['WORKERFS']
   FS.mkdir('/share');
-  FS.mount(FS.filesystems['WORKERFS'], {
+  FS.mount(WORKERFS, {
     packages: [{ metadata: fsMeta[name], blob: fsBlob[name] }]
   }, '/share');
+  // fix for slow Blob operations by caching typed arrays
+  // https://github.com/kripken/emscripten/blob/incoming/src/library_workerfs.js
+  var reader = WORKERFS.reader;
+  var blobcache = {};
+  WORKERFS.stream_ops.read = function (stream, buffer, offset, length, position) {
+    if (position >= stream.node.size) return 0;
+    var contents = blobcache[stream.path];
+    if (!contents) {
+      var ab = reader.readAsArrayBuffer(stream.node.contents);
+      contents = blobcache[stream.path] = new Uint8Array(ab);
+    }
+    if (position + length > contents.length)
+      length = contents.length - position;
+    for (var i=0; i<length; i++) {
+      buffer[offset+i] = contents[position+i];
+    }
+    return length;
+  };
 }
 
 var print_fn = function(s) {
diff --git a/test/cli/teststore.js b/test/cli/teststore.js
index 96c6fe13..184eaf3c 100644
--- a/test/cli/teststore.js
+++ b/test/cli/teststore.js
@@ -63,8 +63,12 @@ describe('Store', function() {
     assert.equal('true', localItems['__migrated__TEST']);
     store.getItem('test', function(err, result) {
       if (err) done(err);
+      // did it convert?
       assert.equal(result, 'a');
       assert.equal(7, localMods);
+      // did we not mess with original storage?
+      assert.equal(localStorage.getItem('_TEST/test'), 'a');
+      assert.equal(localStorage.getItem('_TEST/local/test'), 'b');
       done();
     });
    });