--- a/gfx/layers/Compositor.cpp
+++ b/gfx/layers/Compositor.cpp
@@ -82,17 +82,17 @@ Compositor::NotifyNotUsedAfterCompositio
 
   mNotifyNotUsedAfterComposition.AppendElement(aTextureHost);
 
   // If Compositor holds many TextureHosts without compositing,
   // the TextureHosts should be flushed to reduce memory consumption.
   const int thresholdCount = 5;
   const double thresholdSec = 2.0f;
   if (mNotifyNotUsedAfterComposition.Length() > thresholdCount) {
-    TimeDuration duration = TimeStamp::Now() - mLastCompositionEndTime;
+    TimeDuration duration = mLastCompositionEndTime ? TimeStamp::Now() - mLastCompositionEndTime : TimeDuration();
     // Check if we could flush
     if (duration.ToSeconds() > thresholdSec) {
       FlushPendingNotifyNotUsed();
     }
   }
 }
 
 void