diff --git a/src/borg/archiver.py b/src/borg/archiver.py
index 50540369c..2604818d8 100644
--- a/src/borg/archiver.py
+++ b/src/borg/archiver.py
@@ -30,7 +30,7 @@ from .constants import *  # NOQA
 from .helpers import EXIT_SUCCESS, EXIT_WARNING, EXIT_ERROR
 from .helpers import Error, NoManifestError
 from .helpers import location_validator, archivename_validator, ChunkerParams, CompressionSpec
-from .helpers import PrefixSpec, sort_by_spec, HUMAN_SORT_KEYS
+from .helpers import prefix_spec, sort_by_spec, HUMAN_SORT_KEYS
 from .helpers import BaseFormatter, ItemFormatter, ArchiveFormatter, format_time, format_file_size, format_archive
 from .helpers import safe_encode, remove_surrogates, bin_to_hex
 from .helpers import prune_within, prune_split
@@ -1605,7 +1605,7 @@ class Archiver:
         subparser.add_argument('--last', dest='last',
                                type=int, default=None, metavar='N',
                                help='only check last N archives (Default: all)')
-        subparser.add_argument('-P', '--prefix', dest='prefix', type=PrefixSpec,
+        subparser.add_argument('-P', '--prefix', dest='prefix', type=prefix_spec,
                                help='only consider archive names starting with this prefix')
         subparser.add_argument('-p', '--progress', dest='progress',
                                action='store_true', default=False,
@@ -1995,7 +1995,7 @@ class Archiver:
         subparser.add_argument('--format', '--list-format', dest='format', type=str,
                                help="""specify format for file listing
                                 (default: "{mode} {user:6} {group:6} {size:8d} {isomtime} {path}{extra}{NL}")""")
-        subparser.add_argument('-P', '--prefix', dest='prefix', type=PrefixSpec,
+        subparser.add_argument('-P', '--prefix', dest='prefix', type=prefix_spec,
                                help='only consider archive names starting with this prefix')
         subparser.add_argument('-e', '--exclude', dest='excludes',
                                type=parse_pattern, action='append',
@@ -2161,7 +2161,7 @@ class Archiver:
                                help='number of monthly archives to keep')
         subparser.add_argument('-y', '--keep-yearly', dest='yearly', type=int, default=0,
                                help='number of yearly archives to keep')
-        subparser.add_argument('-P', '--prefix', dest='prefix', type=PrefixSpec,
+        subparser.add_argument('-P', '--prefix', dest='prefix', type=prefix_spec,
                                help='only consider archive names starting with this prefix')
         subparser.add_argument('--save-space', dest='save_space', action='store_true',
                                default=False,
@@ -2634,7 +2634,7 @@ class Archiver:
         if args.location.archive:
             raise Error('The options --first, --last and --prefix can only be used on repository targets.')
 
-        archives = manifest.archives.list()
+        archives = manifest.archives.list(prefix=args.prefix)
         if not archives:
             logger.critical('There are no archives.')
             self.exit_code = self.exit_code or EXIT_WARNING
@@ -2645,7 +2645,7 @@ class Archiver:
         if args.last:
             archives.reverse()
 
-        n = args.first or args.last
+        n = args.first or args.last or len(archives)
 
         return archives[:n]
 
diff --git a/src/borg/helpers.py b/src/borg/helpers.py
index 85959e864..27ce121b9 100644
--- a/src/borg/helpers.py
+++ b/src/borg/helpers.py
@@ -142,11 +142,11 @@ class Archives(abc.MutableMapping):
         name = safe_encode(name)
         del self._archives[name]
 
-    def list(self, sort_by=None, reverse=False):
+    def list(self, sort_by=None, reverse=False, prefix=''):
         """ Inexpensive Archive.list_archives replacement if we just need .name, .id, .ts
             Returns list of borg.helpers.ArchiveInfo instances
         """
-        archives = list(self.values())  # [self[name] for name in self]
+        archives = [x for x in self.values() if x.name.startswith(prefix)]
         if sort_by is not None:
             archives = sorted(archives, key=attrgetter(sort_by))
         if reverse:
@@ -572,10 +572,6 @@ def CompressionSpec(s):
     raise ValueError
 
 
-def PrefixSpec(s):
-    return replace_placeholders(s)
-
-
 def dir_is_cachedir(path):
     """Determines whether the specified path is a cache directory (and
     therefore should potentially be excluded from the backup) according to
@@ -658,10 +654,13 @@ def replace_placeholders(text):
     }
     return format_line(text, data)
 
+prefix_spec = replace_placeholders
+
 
 HUMAN_SORT_KEYS = ['timestamp'] + list(ArchiveInfo._fields)
 HUMAN_SORT_KEYS.remove('ts')
 
+
 def sort_by_spec(text):
     for token in text.split(','):
         if token not in HUMAN_SORT_KEYS: