A clamping collar comprising a looped metal strap (10), and a transverse buckle (12) retained at the first end of the strap. On the outer side, the buckle forms a passage (13) through which the second end of the strap (10B) is inserted. The buckle has an inner portion (14) that is disposed against the inner face of the first end of the strap and that has a blocking transverse edge (14A) that co-operates with a blocking transverse stop (16A) of the first end of the strap that defines a blocking setback (16). The second end (10B) of the strap has a retaining transverse stop (11) received in the blocking setback (16) and co-operating in abutment with a retaining edge (17A) of said blocking setback to retain the second end of the strap to prevent it from moving in the direction in which the diameter of the collar increases.