diff --git a/modules/libpr0n/src/imgContainer.cpp b/modules/libpr0n/src/imgContainer.cpp
index 8fc25986647f..d1d1e90d37f1 100644
--- a/modules/libpr0n/src/imgContainer.cpp
+++ b/modules/libpr0n/src/imgContainer.cpp
@@ -1736,7 +1736,9 @@ void imgContainer::ClearFrame(imgFrame *aFrame)
   if (!aFrame)
     return;
 
-  aFrame->LockImageData();
+  nsresult rv = aFrame->LockImageData();
+  if (NS_FAILED(rv))
+    return;
 
   nsRefPtr<gfxASurface> surf;
   aFrame->GetSurface(getter_AddRefs(surf));
@@ -1755,7 +1757,9 @@ void imgContainer::ClearFrame(imgFrame *aFrame, nsIntRect &aRect)
   if (!aFrame || aRect.width <= 0 || aRect.height <= 0)
     return;
 
-  aFrame->LockImageData();
+  nsresult rv = aFrame->LockImageData();
+  if (NS_FAILED(rv))
+    return;
 
   nsRefPtr<gfxASurface> surf;
   aFrame->GetSurface(getter_AddRefs(surf));
diff --git a/modules/libpr0n/src/imgFrame.cpp b/modules/libpr0n/src/imgFrame.cpp
index 4b140961f208..229a42b5a772 100644
--- a/modules/libpr0n/src/imgFrame.cpp
+++ b/modules/libpr0n/src/imgFrame.cpp
@@ -811,7 +811,7 @@ void imgFrame::GetPaletteData(PRUint32 **aPalette, PRUint32 *length) const
 nsresult imgFrame::LockImageData()
 {
   if (mPalettedImageData)
-    return NS_OK;
+    return NS_ERROR_NOT_AVAILABLE;
 
   if ((mOptSurface || mSinglePixel) && !mImageSurface) {
     // Recover the pixels
@@ -843,7 +843,7 @@ nsresult imgFrame::LockImageData()
 nsresult imgFrame::UnlockImageData()
 {
   if (mPalettedImageData)
-    return NS_OK;
+    return NS_ERROR_NOT_AVAILABLE;
 
 #ifdef XP_MACOSX
   if (mQuartzSurface)