-(defconstant-eqx sc-offset-scn-byte (byte 5 0) #'equalp)
-(defconstant-eqx sc-offset-offset-byte (byte 22 5) #'equalp)
+;;;; FIXME: this layout is hardcoded in some .S files,
+;;;; undefined_tramp in at least ppc-assem.S and mips-assem.S uses it.
+;;;; Ideally, it shouldn't be hardcoded.
+(defconstant-eqx sc-offset-scn-byte (byte 6 0) #'equalp)
+(defconstant-eqx sc-offset-offset-byte (byte 21 6) #'equalp)