Late filling of return-dis-allowances of current years loss or c/f losses too

The assessee failed to file return on or before due date in AY 2017-18.

Assessee has b/f absorbed losses Rs. 5 lakh in the beginning

Assessee incurred losses in AY 2017-18 Rs. 1 lakh

will assessee be allowed to c/f 6 lakh for next AY or he will be allowed only 5 lakh to be C/f

Assessing officer denied to allow the whole Rs 6 lakh to c/f. Is AO correct ?