diff --git a/effects.go b/effects.go
index 17089e1..19dbc31 100644
--- a/effects.go
+++ b/effects.go
@@ -138,8 +138,20 @@ func Median(img image.Image, size int) *image.RGBA {
 				i := 0
 				for ky := 0; ky < size; ky++ {
 					for kx := 0; kx < size; kx++ {
-						ix := (x - size/2 + kx + w) % (w)
-						iy := (y - size/2 + ky + h) % h
+						ix := x - size/2 + kx
+						iy := y - size/2 + ky
+
+						if ix < 0 {
+							ix = 0
+						} else if ix >= w {
+							ix = w - 1
+						}
+
+						if iy < 0 {
+							iy = 0
+						} else if iy >= h {
+							iy = h - 1
+						}
 
 						ipos := iy*dst.Stride + ix*4
 						neighbors[i] = color.RGBA{
diff --git a/effects_test.go b/effects_test.go
index 84ff84e..e9073d0 100644
--- a/effects_test.go
+++ b/effects_test.go
@@ -341,9 +341,9 @@ func TestMedian(t *testing.T) {
 				Rect:   image.Rect(0, 0, 3, 3),
 				Stride: 3 * 4,
 				Pix: []uint8{
-					0xff, 0x00, 0x00, 0xff, 0xff, 0x00, 0x00, 0xff, 0xff, 0x00, 0x00, 0xff,
-					0xff, 0x00, 0x00, 0xff, 0xff, 0x00, 0x00, 0xff, 0xff, 0x00, 0x00, 0xff,
-					0xff, 0x00, 0x00, 0xff, 0xff, 0x00, 0x00, 0xff, 0xff, 0x00, 0x00, 0xff,
+					0xFF, 0x0, 0x0, 0xFF, 0xFF, 0x0, 0x0, 0xFF, 0xFF, 0x0, 0x0, 0xFF,
+					0xFF, 0x0, 0x0, 0xFF, 0xFF, 0x0, 0x0, 0xFF, 0xFF, 0x0, 0x0, 0xFF,
+					0x0, 0xFF, 0x0, 0xFF, 0xFF, 0x0, 0x0, 0xFF, 0xFF, 0x0, 0x0, 0xFF,
 				},
 			},
 		},
@@ -352,7 +352,7 @@ func TestMedian(t *testing.T) {
 	for _, c := range cases {
 		actual := Median(c.value, c.size)
 		if !rgbaImageEqual(actual, c.expected) {
-			t.Error(testFailMessage("Sobel", c.expected, actual))
+			t.Error(testFailMessage("Sobel", formatImageString(c.expected), formatImageString(actual)))
 		}
 	}
 }