diff --git a/SkGifImageReader.cpp b/SkGifImageReader.cpp
index f0184cb..6d37d59 100644
--- a/SkGifImageReader.cpp
+++ b/SkGifImageReader.cpp
@@ -767,6 +767,12 @@
             if (currentFrameIsFirstFrame()) {
                 fScreenHeight = std::max(fScreenHeight, yOffset + height);
                 fScreenWidth = std::max(fScreenWidth, xOffset + width);
+            } else {
+                // If a non-first frame is offscreen, it will have no effect on
+                // the output image. Modify its offsets to be consistent with
+                // the Wuffs implementation.
+                if (xOffset > fScreenWidth) xOffset = fScreenWidth;
+                if (yOffset > fScreenHeight) yOffset = fScreenHeight;
             }
 
             // NOTE: Chromium placed this block after setHeaderDefined, down
@@ -814,7 +820,8 @@
                 return SkCodec::kSuccess;
             }
 
-
+            width  = std::min(width,  fScreenWidth  - xOffset);
+            height = std::min(height, fScreenHeight - yOffset);
             currentFrame->setXYWH(xOffset, yOffset, width, height);
             currentFrame->setInterlaced(SkToBool(currentComponent[8] & 0x40));
 
diff --git a/SkLibGifCodec.cpp b/SkLibGifCodec.cpp
index 71d0e81..b76c18f 100644
--- a/SkLibGifCodec.cpp
+++ b/SkLibGifCodec.cpp
@@ -225,12 +225,9 @@
     // This is only called by prepareToDecode, which ensures frameIndex is in range.
     SkASSERT(frame);
 
-    const int xBegin = frame->xOffset();
-    const int xEnd = std::min(frame->frameRect().right(), fReader->screenWidth());
-
-    // CreateSwizzler only reads left and right of the frame. We cannot use the frame's raw
-    // frameRect, since it might extend beyond the edge of the frame.
-    SkIRect swizzleRect = SkIRect::MakeLTRB(xBegin, 0, xEnd, 0);
+    // Swizzler::Make only reads left and right of this rect.
+    SkIRect swizzleRect = frame->frameRect();
+    SkASSERT(swizzleRect.right() <= fReader->screenWidth());
 
     SkImageInfo swizzlerInfo = dstInfo;
     if (this->colorXform()) {
@@ -407,15 +404,15 @@
     const SkGIFFrameContext* frameContext = fReader->frameContext(frameIndex);
     // The pixel data and coordinates supplied to us are relative to the frame's
     // origin within the entire image size, i.e.
-    // (frameContext->xOffset, frameContext->yOffset). There is no guarantee
-    // that width == (size().width() - frameContext->xOffset), so
-    // we must ensure we don't run off the end of either the source data or the
-    // row's X-coordinates.
+    // (frameContext->xOffset, frameContext->yOffset).
     const int width = frameContext->width();
     const int xBegin = frameContext->xOffset();
     const int yBegin = frameContext->yOffset() + rowNumber;
-    const int xEnd = std::min(xBegin + width, this->dimensions().width());
+    const int xEnd = xBegin + width;
     const int yEnd = std::min(yBegin + repeatCount, this->dimensions().height());
+
+    SkASSERT(xEnd <= this->dimensions().width());
+
     // FIXME: No need to make the checks on width/xBegin/xEnd for every row. We could instead do
     // this once in prepareToDecode.
     if (!width || (xBegin < 0) || (yBegin < 0) || (xEnd <= xBegin) || (yEnd <= yBegin))