diff --git a/makefile.bootstrapit.make b/makefile.bootstrapit.make
index ac91372..74a60fb 100644
--- a/makefile.bootstrapit.make
+++ b/makefile.bootstrapit.make
@@ -336,6 +336,15 @@ lint_flake8:
 	@printf "\e[1F\e[9C ok\n"
 
 
+## Run pylint.
+.PHONY: lint_pylint_errors
+lint_pylint_errors:
+	@printf "pylint ..\n";
+	@$(DEV_ENV)/bin/pylint --errors-only --jobs=4 --rcfile=setup.cfg \
+		src/ test/
+	@printf "\e[1F\e[9C ok\n"
+
+
 ## Run pylint.
 .PHONY: lint_pylint
 lint_pylint:
diff --git a/src/pycalver/v2version.py b/src/pycalver/v2version.py
index dabcd53..4ee941d 100644
--- a/src/pycalver/v2version.py
+++ b/src/pycalver/v2version.py
@@ -628,7 +628,7 @@ def _incr_numeric(
     return cur_vinfo
 
 
-def is_valid_week_pattern(raw_pattern) -> bool:
+def is_valid_week_pattern(raw_pattern: str) -> bool:
     has_yy_part = any(part in raw_pattern for part in ["YYYY", "YY", "0Y"])
     has_ww_part = any(part in raw_pattern for part in ["WW"  , "0W", "UU", "0U"])
     has_gg_part = any(part in raw_pattern for part in ["GGGG", "GG", "0G"])