WebGL: How to correctly blend alpha channel png

Question

I'm pretty new to OpenGL and even newer to WebGL. I'm trying to draw a textured quad with an alpha channel. However I just can't get the blending right.

This is the result I'm looking for

And this is what the WebGL result looks like

As you can see there is kind of a white outline on the dice edges, where in the original image, there is not.

This is how I do my blending in WebGL

gl.clearColor(0.5, 0.5, 0.5, 1);
gl.disable(gl.DEPTH_TEST);
gl.enable(gl.BLEND);
gl.blendFunc(gl.SRC_ALPHA, gl.ONE_MINUS_SRC_ALPHA);

Here is my fragment shader:

precision mediump float;

varying vec2 vUV;

uniform sampler2D texture;

void main(void) {
    vec4 frag = texture2D(texture, vUV);
    gl_FragColor = frag;
}

Any idea why this is happening? I'm not creating mipmaps, BTW.