diff --git a/src/image/gif/reader.go b/src/image/gif/reader.go
index 07adeb3a94..bd452eba72 100644
--- a/src/image/gif/reader.go
+++ b/src/image/gif/reader.go
@@ -430,10 +430,13 @@ type GIF struct {
 	Disposal []byte
 	// Config is the global color map (palette), width and height. A nil or
 	// empty-color.Palette Config.ColorModel means that each frame has its own
-	// color map and there is no global color map. For backwards compatibility,
-	// a zero-valued Config is valid to pass to EncodeAll, and implies that the
-	// overall GIF's width and height equals the first frame's width and
-	// height.
+	// color map and there is no global color map. Each frame's bounds must be
+	// within the rectangle defined by the two points (0, 0) and (Config.Width,
+	// Config.Height).
+	//
+	// For backwards compatibility, a zero-valued Config is valid to pass to
+	// EncodeAll, and implies that the overall GIF's width and height equals
+	// the first frame's bounds' Rectangle.Max point.
 	Config image.Config
 	// BackgroundIndex is the background index in the global color map, for use
 	// with the DisposalBackground disposal method.
diff --git a/src/image/gif/writer.go b/src/image/gif/writer.go
index a70fc4079a..322b353fcb 100644
--- a/src/image/gif/writer.go
+++ b/src/image/gif/writer.go
@@ -191,6 +191,10 @@ func (e *encoder) writeImageBlock(pm *image.Paletted, delay int, disposal byte)
 		e.err = errors.New("gif: image block is too large to encode")
 		return
 	}
+	if !b.In(image.Rectangle{Max: image.Point{e.g.Config.Width, e.g.Config.Height}}) {
+		e.err = errors.New("gif: image block is out of bounds")
+		return
+	}
 
 	transparentIndex := -1
 	for i, c := range pm.Palette {
@@ -297,9 +301,9 @@ func EncodeAll(w io.Writer, g *GIF) error {
 		return errors.New("gif: mismatched image and disposal lengths")
 	}
 	if e.g.Config == (image.Config{}) {
-		b := g.Image[0].Bounds()
-		e.g.Config.Width = b.Dx()
-		e.g.Config.Height = b.Dy()
+		p := g.Image[0].Bounds().Max
+		e.g.Config.Width = p.X
+		e.g.Config.Height = p.Y
 	} else if e.g.Config.ColorModel != nil {
 		if _, ok := e.g.Config.ColorModel.(color.Palette); !ok {
 			return errors.New("gif: GIF color model must be a color.Palette")
diff --git a/src/image/gif/writer_test.go b/src/image/gif/writer_test.go
index 2248ac307a..d661015b17 100644
--- a/src/image/gif/writer_test.go
+++ b/src/image/gif/writer_test.go
@@ -297,8 +297,66 @@ func TestEncodeZeroGIF(t *testing.T) {
 	}
 }
 
-// TODO: add test for when individual frames are out of the global bounds.
-// TODO: add test for when the first frame's bounds are not the same as the global bounds.
+func TestEncodeFrameOutOfBounds(t *testing.T) {
+	images := []*image.Paletted{
+		image.NewPaletted(image.Rect(0, 0, 5, 5), palette.Plan9),
+		image.NewPaletted(image.Rect(2, 2, 8, 8), palette.Plan9),
+		image.NewPaletted(image.Rect(3, 3, 4, 4), palette.Plan9),
+	}
+	for _, upperBound := range []int{6, 10} {
+		g := &GIF{
+			Image:    images,
+			Delay:    make([]int, len(images)),
+			Disposal: make([]byte, len(images)),
+			Config: image.Config{
+				Width:  upperBound,
+				Height: upperBound,
+			},
+		}
+		err := EncodeAll(ioutil.Discard, g)
+		if upperBound >= 8 {
+			if err != nil {
+				t.Errorf("upperBound=%d: %v", upperBound, err)
+			}
+		} else {
+			if err == nil {
+				t.Errorf("upperBound=%d: got nil error, want non-nil", upperBound)
+			}
+		}
+	}
+}
+
+func TestEncodeImplicitConfigSize(t *testing.T) {
+	// For backwards compatibility for Go 1.4 and earlier code, the Config
+	// field is optional, and if zero, the width and height is implied by the
+	// first (and in this case only) frame's width and height.
+	//
+	// A Config only specifies a width and height (two integers) while an
+	// image.Image's Bounds method returns an image.Rectangle (four integers).
+	// For a gif.GIF, the overall bounds' top-left point is always implicitly
+	// (0, 0), and any frame whose bounds have a negative X or Y will be
+	// outside those overall bounds, so encoding should fail.
+	for _, lowerBound := range []int{-1, 0, 1} {
+		images := []*image.Paletted{
+			image.NewPaletted(image.Rect(lowerBound, lowerBound, 4, 4), palette.Plan9),
+		}
+		g := &GIF{
+			Image: images,
+			Delay: make([]int, len(images)),
+		}
+		err := EncodeAll(ioutil.Discard, g)
+		if lowerBound >= 0 {
+			if err != nil {
+				t.Errorf("lowerBound=%d: %v", lowerBound, err)
+			}
+		} else {
+			if err == nil {
+				t.Errorf("lowerBound=%d: got nil error, want non-nil", lowerBound)
+			}
+		}
+	}
+}
+
 // TODO: add test for when a frame has the same color map (palette) as the global one.
 
 func BenchmarkEncode(b *testing.B) {