gentoo perl upgrade slot conflict

# emerge -uavND --quiet world


!!! Multiple package instances within a single package slot have been pulled
!!! into the dependency graph, resulting in a slot conflict:

dev-lang/perl:0

 (dev-lang/perl-5.26.9999:0/5.26::gentoo, ebuild scheduled for merge) pulled in by
   (no parents that aren't satisfied by other packages in this slot)

 (dev-lang/perl-5.24.3:0/5.24::gentoo, ebuild scheduled for merge) pulled in by
   dev-lang/perl:0/5.24=[-build(-)] required by (dev-perl/Authen-SASL-2.160.0-r1:0/0::gentoo, installed)
                ^^^^^^^^                                                                                                                    
   (and 23 more with the same problem)

# emerge -uavND -1 --nodeps dev-lang/perl
These are the packages that would be merged, in order:
[ebuild     U *] dev-lang/perl-5.26.9999:0/5.26::gentoo [5.24.1-r1:0/5.24::gentoo] USE="berkdb gdbm -debug -doc -ithreads" 11754 KiB
Total: 1 package (1 upgrade), Size of downloads: 11754 KiB
Would you like to merge these packages? [Yes/No] yes