I rolled money from my pretax 401(k) to my roth 401(k), but the 1099-R Taxable Amount says "0."

[mapaseka]

I am pretty sure it the taxable amount (box 2a) should have the entire amount of the rollover, but it says "0" and the distribution code in box 7 is "G."

Is this a mistake? And if so, what to do about it?