diff --git a/swh/loader/cvs/cvsclient.py b/swh/loader/cvs/cvsclient.py
--- a/swh/loader/cvs/cvsclient.py
+++ b/swh/loader/cvs/cvsclient.py
@@ -11,7 +11,7 @@
 import socket
 import subprocess
 import tempfile
-from typing import Tuple
+from typing import IO, Tuple
 
 from tenacity import retry
 from tenacity.retry import retry_if_exception_type
@@ -291,12 +291,12 @@
     def __del__(self):
         self.conn_close()
 
-    def _parse_rlog_response(self, fp):
+    def _parse_rlog_response(self, fp: IO[bytes]):
         rlog_output = tempfile.TemporaryFile()
         expect_error = False
-        for line in fp.readlines():
+        for line in fp:
             if expect_error:
-                raise CVSProtocolError("CVS server error: %s" % line)
+                raise CVSProtocolError("CVS server error: %r" % line)
             if line == b"ok\n":
                 break
             elif line[0:2] == b"M ":
@@ -311,7 +311,7 @@
                 expect_error = True
                 continue
             else:
-                raise CVSProtocolError("Bad CVS protocol response: %s" % line)
+                raise CVSProtocolError("Bad CVS protocol response: %r" % line)
         rlog_output.seek(0)
         return rlog_output
 
diff --git a/swh/loader/cvs/loader.py b/swh/loader/cvs/loader.py
--- a/swh/loader/cvs/loader.py
+++ b/swh/loader/cvs/loader.py
@@ -13,7 +13,18 @@
 import subprocess
 import tempfile
 import time
-from typing import Any, BinaryIO, Dict, Iterator, List, Optional, Sequence, Tuple, cast
+from typing import (
+    Any,
+    BinaryIO,
+    Dict,
+    Iterator,
+    List,
+    Optional,
+    Sequence,
+    TextIO,
+    Tuple,
+    cast,
+)
 from urllib.parse import urlparse
 
 import sentry_sdk
@@ -115,7 +126,7 @@
         self._visit_status = "full"
         self.visit_date = visit_date or self.visit_date
         self.cvsroot_path = cvsroot_path
-        self.custom_id_keyword = None
+        self.custom_id_keyword: Optional[str] = None
         self.excluded_keywords: List[str] = []
 
         self.snapshot: Optional[Snapshot] = None
@@ -303,7 +314,7 @@
     def cleanup(self) -> None:
         self.log.debug("cleanup")
 
-    def configure_custom_id_keyword(self, cvsconfig):
+    def configure_custom_id_keyword(self, cvsconfig: TextIO):
         """Parse CVSROOT/config and look for a custom keyword definition.
         There are two different configuration directives in use for this purpose.
 
@@ -322,7 +333,7 @@
         For example, this disables expansion of the Date and Name keywords:
         KeywordExpand=eDate,Name
         """
-        for line in cvsconfig.readlines():
+        for line in cvsconfig:
             line = line.strip()
             try:
                 (config_key, value) = line.split("=", 1)
@@ -542,11 +553,11 @@
                 # Combine all the rlog pieces we found and re-parse.
                 fp = tempfile.TemporaryFile()
                 for attic_rlog_file in attic_rlog_files:
-                    for line in attic_rlog_file.readlines():
+                    for line in attic_rlog_file:
                         fp.write(line)
-                        attic_rlog_file.close()
+                    attic_rlog_file.close()
                 main_rlog_file.seek(0)
-                for line in main_rlog_file.readlines():
+                for line in main_rlog_file:
                     fp.write(line)
                 main_rlog_file.close()
                 fp.seek(0)
diff --git a/swh/loader/cvs/tests/test_loader.py b/swh/loader/cvs/tests/test_loader.py
--- a/swh/loader/cvs/tests/test_loader.py
+++ b/swh/loader/cvs/tests/test_loader.py
@@ -1175,7 +1175,7 @@
     rlog_file_path = rlog_file.name
 
     rlog_weird_paths = open(os.path.join(datadir, rlog_unsafe_path))
-    for line in rlog_weird_paths.readlines():
+    for line in rlog_weird_paths:
         rlog_file.write(line.replace("{cvsroot_path}", os.path.dirname(repo_url[7:])))
     rlog_file.close()
     rlog_file_override = open(rlog_file_path, "rb")  # re-open as bytes instead of str