diff --git a/README.rst b/README.rst
index 5fc9551..a03630d 100644
--- a/README.rst
+++ b/README.rst
@@ -5,6 +5,11 @@ RateLimiter
 
 Simple Python module providing rate limiting.
 
+Fork
+----
+Changes according to the comments in this thread: `https://github.com/RazerM/ratelimiter/issues/15 <https://github.com/RazerM/ratelimiter/issues/15>`_
+
+
 Overview
 --------
 
diff --git a/ratelimiter/_async.py b/ratelimiter/_async.py
index feb80ad..69dc5c1 100644
--- a/ratelimiter/_async.py
+++ b/ratelimiter/_async.py
@@ -23,12 +23,15 @@ async def __aenter__(self):
             # We want to ensure that no more than max_calls were run in the allowed
             # period. For this, we store the last timestamps of each call and run
             # the rate verification upon each __enter__ call.
-            if len(self.calls) >= self.max_calls:
-                until = time.time() + self.period - self._timespan
-                if self.callback:
-                    asyncio.ensure_future(self.callback(until))
+            
+            if len(self.calls) == self.max_calls:
+                until = self.period + self.calls[0]
                 sleeptime = until - time.time()
+
                 if sleeptime > 0:
+                    if self.callback:
+                        asyncio.ensure_future(self.callback(until))
+
                     await asyncio.sleep(sleeptime)
             return self
 
diff --git a/ratelimiter/_sync.py b/ratelimiter/_sync.py
index 577dfb4..ca0bcd9 100644
--- a/ratelimiter/_sync.py
+++ b/ratelimiter/_sync.py
@@ -23,7 +23,7 @@ def __init__(self, max_calls, period=1.0, callback=None):
 
         # We're using a deque to store the last execution timestamps, not for
         # its maxlen attribute, but to allow constant time front removal.
-        self.calls = collections.deque()
+        self.calls = collections.deque(maxlen=max_calls)
 
         self.period = period
         self.max_calls = max_calls
@@ -49,14 +49,18 @@ def __enter__(self):
             # We want to ensure that no more than max_calls were run in the allowed
             # period. For this, we store the last timestamps of each call and run
             # the rate verification upon each __enter__ call.
-            if len(self.calls) >= self.max_calls:
-                until = time.time() + self.period - self._timespan
-                if self.callback:
-                    t = threading.Thread(target=self.callback, args=(until,))
-                    t.daemon = True
-                    t.start()
+            if len(self.calls) == self.max_calls:
+                until = self.period + self.calls[0]
                 sleeptime = until - time.time()
+                
+                print('sleeptime', sleeptime, self.calls[0])
+
                 if sleeptime > 0:
+                    if self.callback:
+                        t = threading.Thread(target=self.callback, args=(until,))
+                        t.daemon = True
+                        t.start()
+
                     time.sleep(sleeptime)
             return self