diff --git a/image/src/imgStatusTracker.cpp b/image/src/imgStatusTracker.cpp
index 379e57693020..d531936e5109 100644
--- a/image/src/imgStatusTracker.cpp
+++ b/image/src/imgStatusTracker.cpp
@@ -146,7 +146,6 @@ imgStatusTracker::imgStatusTracker(Image* aImage)
   : mImage(aImage),
     mState(0),
     mImageStatus(imgIRequest::STATUS_NONE),
-    mHadLastPart(false),
     mHasBeenDecoded(false)
 {
   mTrackerObserver = new imgStatusTrackerObserver(this);
@@ -157,7 +156,6 @@ imgStatusTracker::imgStatusTracker(const imgStatusTracker& aOther)
   : mImage(aOther.mImage),
     mState(aOther.mState),
     mImageStatus(aOther.mImageStatus),
-    mHadLastPart(aOther.mHadLastPart),
     mHasBeenDecoded(aOther.mHasBeenDecoded)
     // Note: we explicitly don't copy several fields:
     //  - mRequestRunnable, because it won't be nulled out when the
@@ -366,7 +364,7 @@ imgStatusTracker::NotifyCurrentState(imgRequestProxy* proxy)
 /* static */ void
 imgStatusTracker::SyncNotifyState(ProxyArray& proxies,
                                   bool hasImage, uint32_t state,
-                                  nsIntRect& dirtyRect, bool hadLastPart)
+                                  nsIntRect& dirtyRect)
 {
   MOZ_ASSERT(NS_IsMainThread());
   // OnStartRequest
@@ -414,7 +412,7 @@ imgStatusTracker::SyncNotifyState(ProxyArray& proxies,
   }
 
   if (state & FLAG_REQUEST_STOPPED) {
-    NOTIFY_IMAGE_OBSERVERS(OnStopRequest(hadLastPart));
+    NOTIFY_IMAGE_OBSERVERS(OnStopRequest(state & FLAG_MULTIPART_STOPPED));
   }
 }
 
@@ -426,8 +424,6 @@ imgStatusTracker::Difference(imgStatusTracker* aOther) const
   diff.diffState = ~mState & aOther->mState & ~FLAG_REQUEST_STARTED;
   diff.diffImageStatus = ~mImageStatus & aOther->mImageStatus;
 
-  diff.foundLastPart = !mHadLastPart && aOther->mHadLastPart;
-
   diff.gotDecoded = !mHasBeenDecoded && aOther->mHasBeenDecoded;
 
   // Only record partial invalidations if we haven't been decoded before.
@@ -471,7 +467,6 @@ imgStatusTracker::ApplyDifference(const ImageStatusDiff& aDiff)
   // Synchronize our state.
   mState |= aDiff.diffState | loadState;
 
-  mHadLastPart = mHadLastPart || aDiff.foundLastPart;
   mHasBeenDecoded = mHasBeenDecoded || aDiff.gotDecoded;
 
   // Update the image status. There are some subtle points which are handled below.
@@ -486,7 +481,7 @@ imgStatusTracker::SyncNotifyDifference(const ImageStatusDiff& diff)
 
   nsIntRect invalidRect = mInvalidRect.Union(diff.invalidRect);
 
-  SyncNotifyState(mConsumers, !!mImage, diff.diffState, invalidRect, mHadLastPart);
+  SyncNotifyState(mConsumers, !!mImage, diff.diffState, invalidRect);
 
   mInvalidRect.SetEmpty();
 
@@ -525,7 +520,7 @@ imgStatusTracker::SyncNotify(imgRequestProxy* proxy)
 
   ProxyArray array;
   array.AppendElement(proxy);
-  SyncNotifyState(array, !!mImage, mState, r, mHadLastPart);
+  SyncNotifyState(array, !!mImage, mState, r);
 }
 
 void
@@ -609,9 +604,10 @@ void
 imgStatusTracker::RecordLoaded()
 {
   NS_ABORT_IF_FALSE(mImage, "RecordLoaded called before we have an Image");
-  mState |= FLAG_REQUEST_STARTED | FLAG_HAS_SIZE | FLAG_REQUEST_STOPPED;
-  mImageStatus |= imgIRequest::STATUS_SIZE_AVAILABLE | imgIRequest::STATUS_LOAD_COMPLETE;
-  mHadLastPart = true;
+  mState |= FLAG_REQUEST_STARTED | FLAG_HAS_SIZE |
+            FLAG_REQUEST_STOPPED | FLAG_MULTIPART_STOPPED;
+  mImageStatus |= imgIRequest::STATUS_SIZE_AVAILABLE |
+                  imgIRequest::STATUS_LOAD_COMPLETE;
 }
 
 void
@@ -826,8 +822,10 @@ void
 imgStatusTracker::RecordStopRequest(bool aLastPart,
                                     nsresult aStatus)
 {
-  mHadLastPart = aLastPart;
   mState |= FLAG_REQUEST_STOPPED;
+  if (aLastPart) {
+    mState |= FLAG_MULTIPART_STOPPED;
+  }
 
   // If we were successful in loading, note that the image is complete.
   if (NS_SUCCEEDED(aStatus)) {
diff --git a/image/src/imgStatusTracker.h b/image/src/imgStatusTracker.h
index 7c73cb242c52..edc87999d6af 100644
--- a/image/src/imgStatusTracker.h
+++ b/image/src/imgStatusTracker.h
@@ -38,7 +38,8 @@ enum {
   FLAG_ONLOAD_BLOCKED     = 1u << 6,
   FLAG_ONLOAD_UNBLOCKED   = 1u << 7,
   FLAG_IS_ANIMATED        = 1u << 8,
-  FLAG_IS_MULTIPART       = 1u << 9
+  FLAG_IS_MULTIPART       = 1u << 9,
+  FLAG_MULTIPART_STOPPED  = 1u << 10
 };
 
 struct ImageStatusDiff
@@ -47,7 +48,6 @@ struct ImageStatusDiff
     : invalidRect()
     , diffState(0)
     , diffImageStatus(0)
-    , foundLastPart(false)
     , gotDecoded(false)
   { }
 
@@ -59,7 +59,6 @@ struct ImageStatusDiff
     return aOther.invalidRect == invalidRect
         && aOther.diffState == diffState
         && aOther.diffImageStatus == diffImageStatus
-        && aOther.foundLastPart == foundLastPart
         && aOther.gotDecoded == gotDecoded;
   }
 
@@ -67,14 +66,12 @@ struct ImageStatusDiff
     invalidRect = invalidRect.Union(aOther.invalidRect);
     diffState |= aOther.diffState;
     diffImageStatus |= aOther.diffImageStatus;
-    foundLastPart = foundLastPart || aOther.foundLastPart;
     gotDecoded = gotDecoded || aOther.gotDecoded;
   }
 
   nsIntRect invalidRect;
   uint32_t  diffState;
   uint32_t  diffImageStatus;
-  bool      foundLastPart      : 1;
   bool      gotDecoded         : 1;
 };
 
@@ -294,7 +291,7 @@ private:
   // thread, and mConsumers is not threadsafe.
   static void SyncNotifyState(ProxyArray& proxies,
                               bool hasImage, uint32_t state,
-                              nsIntRect& dirtyRect, bool hadLastPart);
+                              nsIntRect& dirtyRect);
 
   nsCOMPtr<nsIRunnable> mRequestRunnable;
 
@@ -314,7 +311,6 @@ private:
 
   uint32_t mState;
   uint32_t mImageStatus;
-  bool mHadLastPart    : 1;
   bool mHasBeenDecoded : 1;
 };