diff --git a/src/calibre/utils/resources.py b/src/calibre/utils/resources.py
index 7ec24aa776..c2dc580b3f 100644
--- a/src/calibre/utils/resources.py
+++ b/src/calibre/utils/resources.py
@@ -77,12 +77,15 @@ def get_image_path(path, data=False, allow_user_override=True):
         return get_path('images', allow_user_override=allow_user_override)
     return get_path('images/'+path, data=data, allow_user_override=allow_user_override)
 
-def _compile_coffeescript(name):
-    from calibre.utils.serve_coffee import compile_coffeescript
-    path = (u'/'.join(name.split('.'))) + '.coffee'
+def js_name_to_path(name, ext='.coffee'):
+    path = (u'/'.join(name.split('.'))) + ext
     d = os.path.dirname
     base = d(d(os.path.abspath(__file__)))
-    src = os.path.join(base, path)
+    return os.path.join(base, path)
+
+def _compile_coffeescript(name):
+    from calibre.utils.serve_coffee import compile_coffeescript
+    src = js_name_to_path(name)
     with open(src, 'rb') as f:
         cs, errors = compile_coffeescript(f.read(), src)
         if errors:
@@ -93,12 +96,19 @@ def _compile_coffeescript(name):
         return cs
 
 def compiled_coffeescript(name, dynamic=False):
-    if dynamic:
-        return _compile_coffeescript(name)
-    else:
-        import zipfile
-        zipf = get_path('compiled_coffeescript.zip', allow_user_override=False)
-        with zipfile.ZipFile(zipf, 'r') as zf:
+    import zipfile
+    zipf = get_path('compiled_coffeescript.zip', allow_user_override=False)
+    with zipfile.ZipFile(zipf, 'r') as zf:
+        if dynamic:
+            import json
+            existing_hash = json.loads(zf.comment or '{}').get(name + '.js')
+            if existing_hash is not None:
+                import hashlib
+                with open(js_name_to_path(name), 'rb') as f:
+                    if existing_hash == hashlib.sha1(f.read()).hexdigest():
+                        return zf.read(name + '.js')
+            return _compile_coffeescript(name)
+        else:
             return zf.read(name+'.js')
 
 __builtin__.__dict__['P'] = get_path