Jatukarnya 1.11: Nirṇayasindhu · Bhagavantabhāskara

1.11

pitṛvyabhrātṛmātṝṇām aputrāṇāṃ tathaiva ca | mātāmahasyāsutasya śrāddhādi pitṛvad bhavet

For sonless paternal uncles, brothers, and mothers as well, / and for a sonless maternal grandfather, the śrāddha and other rites should be performed like those for a father.

For sonless paternal uncles, brothers and mothers, and for a sonless maternal grandfather, the śrāddha and the rest are to be as for one's father.