diff --git a/internal/graphics/shader.go b/internal/graphics/shader.go
index 7bb183edd..97b7d8e70 100644
--- a/internal/graphics/shader.go
+++ b/internal/graphics/shader.go
@@ -51,12 +51,19 @@ varying vec2 varying_tex_coord;
 varying vec2 varying_tex_coord_min;
 varying vec2 varying_tex_coord_max;
 
+const float minHighpValue = 1.0 / 32768.0;
+
 void main(void) {
   varying_tex_coord = vec2(tex_coord[0], tex_coord[1]);
-  varying_tex_coord_min =
-    vec2(min(tex_coord[0], tex_coord[2]), min(tex_coord[1], tex_coord[3]));
-  varying_tex_coord_max =
-    vec2(max(tex_coord[0], tex_coord[2]), max(tex_coord[1], tex_coord[3]));
+  // varying_tex_coord_min and varying_tex_coord_max mean endmost texel values
+  // in the source rect. As varying_tex_coord is adjusted with minHighpValue
+  // in vertices.go, re-adjust them so that exact endmost texel values.
+  varying_tex_coord_min = vec2(
+    min(tex_coord[0], tex_coord[2]) - minHighpValue,
+    min(tex_coord[1], tex_coord[3]) - minHighpValue);
+  varying_tex_coord_max = vec2(
+    max(tex_coord[0], tex_coord[2]) + minHighpValue,
+    max(tex_coord[1], tex_coord[3]) + minHighpValue);
   gl_Position = projection_matrix * vec4(vertex, 0, 1);
 }
 `
diff --git a/vertices.go b/vertices.go
index b02f72047..8635d1d82 100644
--- a/vertices.go
+++ b/vertices.go
@@ -87,6 +87,15 @@ func vertices(sx0, sy0, sx1, sy1 int, width, height int, geo *affine.GeoM) []flo
 	hf := float32(h)
 	u0, v0, u1, v1 := float32(sx0)/wf, float32(sy0)/hf, float32(sx1)/wf, float32(sy1)/hf
 
+	// Adjust texels to be slightly inside the source rect. Without this
+	// adjustment, texels can be exactly as same values as the edges'
+	// positions and it could happen that nothing is rendered. (#491)
+	const minHighpValue = 1.0/32768.0
+	u0 += minHighpValue
+	v0 += minHighpValue
+	u1 -= minHighpValue
+	v1 -= minHighpValue
+
 	x, y := geo.Apply32(x0, y0)
 	// Vertex coordinates
 	vs[0] = x