diff --git a/backend/goglbackend/fill.go b/backend/goglbackend/fill.go
index fefd4c0..51afec0 100644
--- a/backend/goglbackend/fill.go
+++ b/backend/goglbackend/fill.go
@@ -175,6 +175,12 @@ func (b *GoGLBackend) FillImageMask(style *backendbase.FillStyle, mask *image.Al
 		off := y * mask.Stride
 		gl.TexSubImage2D(gl.TEXTURE_2D, 0, 0, int32(alphaTexSize-1-y), int32(w), 1, gl.ALPHA, gl.UNSIGNED_BYTE, gl.Ptr(&mask.Pix[off]))
 	}
+	if h < alphaTexSize {
+		gl.TexSubImage2D(gl.TEXTURE_2D, 0, 0, int32(alphaTexSize-1-h), int32(w), 1, gl.ALPHA, gl.UNSIGNED_BYTE, gl.Ptr(&zeroes[0]))
+	}
+	if w < alphaTexSize {
+		gl.TexSubImage2D(gl.TEXTURE_2D, 0, int32(w), int32(alphaTexSize-1-h), 1, int32(h), gl.ALPHA, gl.UNSIGNED_BYTE, gl.Ptr(&zeroes[0]))
+	}
 
 	if style.Blur > 0 {
 		b.offscr1.alpha = true
@@ -215,10 +221,6 @@ func (b *GoGLBackend) FillImageMask(style *backendbase.FillStyle, mask *image.Al
 
 	gl.StencilFunc(gl.ALWAYS, 0, 0xFF)
 
-	for y := 0; y < h; y++ {
-		gl.TexSubImage2D(gl.TEXTURE_2D, 0, 0, int32(alphaTexSize-1-y), int32(w), 1, gl.ALPHA, gl.UNSIGNED_BYTE, gl.Ptr(&zeroes[0]))
-	}
-
 	gl.ActiveTexture(gl.TEXTURE0)
 
 	if style.Blur > 0 {