diff --git a/throttle.go b/throttle.go
index 0e31938..86f2434 100644
--- a/throttle.go
+++ b/throttle.go
@@ -46,22 +46,31 @@ func (t *Throttle) run() {
 			}
 			case r:=<-t.queueChan: {
 				for {
-					if t.config.NumTokens > 0 || t.config.RefillRate == 0 {
-						r.resolveChan <- rxgo.Of(true)
-						close(r.resolveChan)
+					var hasEnoughTokens bool
+					if t.config.Capacity != 0 {
+						hasEnoughTokens = t.config.NumTokens > 0
+					} else {
+						hasEnoughTokens = t.config.NumTokens >= 0
+					}
+					if hasEnoughTokens {
 						var cost float64 = 0
 						if r.cost != -1 {
 							cost = r.cost
 						} else {
 							cost = t.config.DefaultCost
 						}
-						t.config.NumTokens -= cost
-						break
+						if t.config.NumTokens >= math.Min(cost, t.config.Capacity) {
+							t.config.NumTokens -= cost
+							r.resolveChan <- rxgo.Of(true)
+							close(r.resolveChan)
+							break
+						}
 					}
+
 					if t.lastTimestamp == -1 {
-						t.lastTimestamp = time.Now().Unix()
+						t.lastTimestamp = time.Now().UnixNano()
 					}
-					now := time.Now().Unix()
+					now := time.Now().UnixNano()
 					elapsed := now - t.lastTimestamp
 					t.lastTimestamp = now
 					t.config.NumTokens = math.Min(t.config.Capacity, t.config.NumTokens+float64(elapsed)*t.config.RefillRate)
@@ -74,7 +83,7 @@ func (t *Throttle) run() {
 
 }
 
-func (t *Throttle) Take(rateLimit float64, cost float64) rxgo.Observable {
+func (t *Throttle) Take(rateLimit time.Duration, cost float64) rxgo.Observable {
 	t.cfgMut.Lock()
 	defer t.cfgMut.Unlock()
 	ch := make(chan rxgo.Item)
@@ -85,7 +94,7 @@ func (t *Throttle) Take(rateLimit float64, cost float64) rxgo.Observable {
 	if rateLimit == 0 {
 		t.config.RefillRate = 0
 	} else {
-		t.config.RefillRate = 1/rateLimit
+		t.config.RefillRate = float64(1 / rateLimit.Nanoseconds())
 	}
 	return rxgo.FromChannel(ch)
 }