A synthetic frame (1) is described, of which a jamb (5) has a front face (11) and a side face (12) connecting thereto, and of which a sill (3) has a front face (31) and a top face (32), which meet each other at a sill edge (93). The sill has an end (103) which is partly defined by a 45° end face (131) which intersects the front face (31) of the sill (3) according to an intersecting line (135). The jamb has a bottom end (103) which is partly defined by a 45° end face (133) which intersects the front face (11) of the jamb according to an intersecting line (136). The end faces (131 and 133) of the sill and the jamb are welded together, wherein a welding seam (153) directed according to 45° connects the front face (31) of the sill with the front face (11) of the jamb. The front face (11) of the jamb may be provided with a groove (154) in line with the sill edge (93).