diff --git a/renderers-clocks.ts b/renderers-clocks.ts
index ab8add0..fab0159 100644
--- a/renderers-clocks.ts
+++ b/renderers-clocks.ts
@@ -102,7 +102,7 @@ module libjass.renderers {
 		toggle(): void;
 
 		/**
-		 * Enable or disable the renderer.
+		 * Enable or disable the clock.
 		 *
 		 * @param {boolean} enabled If true, the clock is enabled, otherwise it's disabled.
 		 * @return {boolean} True if the clock is now in the given state, false if it was already in that state.
@@ -261,9 +261,7 @@ module libjass.renderers {
 
 			this._enabled = true;
 
-			if (this._nextAnimationFrameRequestId === null) {
-				this._nextAnimationFrameRequestId = requestAnimationFrame(() => this._onTimerTick());
-			}
+			this._startTicking();
 
 			return true;
 		}
@@ -287,10 +285,7 @@ module libjass.renderers {
 
 			this._dispatchEvent(ClockEvent.Stop, []);
 
-			if (this._nextAnimationFrameRequestId !== null) {
-				cancelAnimationFrame(this._nextAnimationFrameRequestId);
-				this._nextAnimationFrameRequestId = null;
-			}
+			this._stopTicking();
 
 			return true;
 		}
@@ -331,9 +326,7 @@ module libjass.renderers {
 				return;
 			}
 
-			if (this._nextAnimationFrameRequestId === null) {
-				this._nextAnimationFrameRequestId = requestAnimationFrame(() => this._onTimerTick());
-			}
+			this._startTicking();
 		}
 
 		private _onVideoPause(): void {
@@ -357,12 +350,7 @@ module libjass.renderers {
 				return;
 			}
 
-			cancelAnimationFrame(this._nextAnimationFrameRequestId);
-			this._nextAnimationFrameRequestId = null;
-
-			if (libjass.verboseMode) {
-				console.log("VideoClock._onVideoPause: Cancelled VideoClock._nextAnimationFrameRequestId");
-			}
+			this._stopTicking();
 		}
 
 		private _onVideoSeeking(): void {
@@ -411,6 +399,19 @@ module libjass.renderers {
 			this._nextAnimationFrameRequestId = requestAnimationFrame(() => this._onTimerTick());
 		}
 
+		private _startTicking(): void {
+			if (this._nextAnimationFrameRequestId === null) {
+				this._nextAnimationFrameRequestId = requestAnimationFrame(() => this._onTimerTick());
+			}
+		}
+
+		private _stopTicking(): void {
+			if (this._nextAnimationFrameRequestId !== null) {
+				cancelAnimationFrame(this._nextAnimationFrameRequestId);
+				this._nextAnimationFrameRequestId = null;
+			}
+		}
+
 		// EventSource members
 		_eventListeners: Map<ClockEvent, Function[]> = new Map<ClockEvent, Function[]>();
 		addEventListener: (type: ClockEvent, listener: Function) => void;
diff --git a/renderers-null.ts b/renderers-null.ts
index 2e0776c..7677f77 100644
--- a/renderers-null.ts
+++ b/renderers-null.ts
@@ -145,7 +145,7 @@ module libjass.renderers {
 		 * Runs when the clock's current time changed. This might be a result of either regular playback or seeking.
 		 */
 		_onClockTick(): void {
-			var currentTime = this.clock.currentTime;
+			var currentTime = this._clock.currentTime;
 
 			if (libjass.verboseMode) {
 				console.log("NullRenderer._onClockTick: currentTime = " + currentTime);