Strange Compile Error when concatenating arrays

[Jeroen Bollen]

When I concatenate arrays like this, I get a strange compile 
error:

Error: incompatible types for ((cast(int)a) ~ (cast(int)b)): 
'int' and 'int'

Code:

public ubyte[] toArray(ubyte a, ubyte b, ubyte c) {
        return a ~ b ~ c;
}