A shoulder injury has kept him out of Glasgow's last two matches.
Calvin replaces Colin Gregor, although the Watsonians' stand-off is among the replacements.
Andy Kelly will again be at loose-head prop following his late call into the team last week after Lee Harrison damaged a hamstring in the warm-up. Euan Murray stays on the tight head.
Joe Beardshaw is at lock because Andy Hall received his third yellow card of the season in the Cardiff match and will serve an automatic one-match suspension.
Tomorrow's match will kick off at 7.30pm.
Glasgow
15 Glenn Metcalfe
14 Rory Kerr
13 Graeme Morrison
12 Alan Bulloch
11 Sean Lamont
10 Calvin Howarth
9 Graeme Beveridge
1 Euan Murray
2 Scott Lawson
3 Andrew Kelly
4 Joe Beardshaw
5 Nathan Ross
6 Paul Dearlove
7 Donnie Macfadyen
8 Jon Petrie (captain)
Substitutes:
16 Simon Gunn
17 Lee Harrison
18 Roland Reid
19 Andrew Wilson
20 Sam Pinder
21 Colin Gregor
22 David Millard