mdlSetDefa​ultPortDim​ensionInfo function does not fully set the dimension

My mdlSetDefaultPortDimensionInfo function looks like this:

static void mdlSetDefaultPortDimensionInfo(SimStruct        *S)
{
    ssSetInputPortWidth(S, 0, 2);
    ssSetOutputPortWidth(S, 0, 1);
}

The Simulink model is just a simple feed-through and looks like this:

When running the Simulink model I get the following error:

Error in default port dimensions function of S-function 'minimal_simulink/S-Function'. This function does not fully set the dimensions of output port 1

The mdloutputs function looks like this:

static void mdlOutputs(SimStruct *S, int_T tid)
{
    const real_T   *u0  = (const real_T*) ssGetInputPortSignal(S,0);
    real_T        *y0  = (real_T *)ssGetOutputPortRealSignal(S,0);
    y0[0] = u0[0];
}

Although in the manual it's stated that the mdlSetDefaultPortDimensionInfo is not required my model does not work without it.

I would be glad if someone could help me to fix this error.