diff --git a/emscripten.py b/emscripten.py
index 5eb62ba22..681d22836 100755
--- a/emscripten.py
+++ b/emscripten.py
@@ -74,6 +74,8 @@ def emscript(infile, settings, outfile, libraries=[]):
 
   if DEBUG: print >> sys.stderr, 'emscript: ll=>js'
 
+  if jcache: JCache.ensure()
+
   # Pre-scan ll and alter settings as necessary
   if DEBUG: t = time.time()
   ll = open(infile).read()
@@ -134,13 +136,14 @@ def emscript(infile, settings, outfile, libraries=[]):
   pre_input = ''.join(pre) + '\n' + meta
   out = None
   if jcache:
-    pre_cache_key = JCache.get_key([pre_input, settings_text, ','.join(libraries)])
-    out = JCache.get(pre_cache_key)
+    keys = [pre_input, settings_text, ','.join(libraries)]
+    shortkey = JCache.get_key(keys)
+    out = JCache.get(shortkey, keys)
   if not out:
     open(pre_file, 'w').write(pre_input)
     out = shared.run_js(compiler, shared.COMPILER_ENGINE, [settings_file, pre_file, 'pre'] + libraries, stdout=subprocess.PIPE, cwd=path_from_root('src'))
     if jcache:
-      JCache.set(pre_cache_key, out)
+      JCache.set(shortkey, keys, out)
   pre, forwarded_data = out.split('//FORWARDED_DATA:')
   forwarded_file = temp_files.get('.json').name
   open(forwarded_file, 'w').write(forwarded_data)
diff --git a/tools/shared.py b/tools/shared.py
index 06cbba682..b445051dc 100644
--- a/tools/shared.py
+++ b/tools/shared.py
@@ -1154,19 +1154,31 @@ class Cache:
     return cachename
 
 class JCache:
-  # Generates a single key from multiple values
-  @staticmethod
-  def get_key(keys):
-    return ''
+  dirname = os.path.join(Cache.dirname, 'jcache')
 
-  # Returns a cached value for a key (from get_key), if it exists
   @staticmethod
-  def get(key):
+  def ensure():
+    Cache.ensure()
+    if not os.path.exists(JCache.dirname):
+      os.makedirs(JCache.dirname)
+
+  @staticmethod
+  def get_shortkey(keys):
+    if type(keys) not in [list, tuple]:
+      keys = [keys]
+    ret = ''
+    for key in keys:
+      ret += md5.md5(key).hexdigest()
+    return ret
+
+  # Returns a cached value, if it exists. Make sure the full key matches
+  @staticmethod
+  def get(shortkey, keys):
     return None
 
   # Sets the cached value for a key (from get_key)
   @staticmethod
-  def set(key, value):
+  def set(shortkey, keys, value):
     pass
 
 # Compression of code and data for smaller downloads