diff --git a/nisaba/scripts/brahmic/iso.py b/nisaba/scripts/brahmic/iso.py
index 02e675fb..b723039f 100644
--- a/nisaba/scripts/brahmic/iso.py
+++ b/nisaba/scripts/brahmic/iso.py
@@ -56,16 +56,16 @@
 
 
 def brahmic_to_iso(
-    consonant_file: os.PathLike,
-    inherent_vowel_file: os.PathLike,
-    vowel_sign_file: os.PathLike,
-    vowel_file: os.PathLike,
-    vowel_length_sign_file: os.PathLike,
-    coda_file: os.PathLike,
-    dead_consonant_file: os.PathLike,
-    standalone_file: os.PathLike,
-    subjoined_consonant_file: os.PathLike,
-    virama_file: os.PathLike,
+    consonant_file: os.PathLike[str],
+    inherent_vowel_file: os.PathLike[str],
+    vowel_sign_file: os.PathLike[str],
+    vowel_file: os.PathLike[str],
+    vowel_length_sign_file: os.PathLike[str],
+    coda_file: os.PathLike[str],
+    dead_consonant_file: os.PathLike[str],
+    standalone_file: os.PathLike[str],
+    subjoined_consonant_file: os.PathLike[str],
+    virama_file: os.PathLike[str],
 ) -> p.Fst:
   """Creates an FST that transduces a Brahmic script to ISO 15919.
 
diff --git a/nisaba/scripts/brahmic/util.py b/nisaba/scripts/brahmic/util.py
index 38f0eddd..f7579b1d 100644
--- a/nisaba/scripts/brahmic/util.py
+++ b/nisaba/scripts/brahmic/util.py
@@ -58,7 +58,7 @@ def OpenSigma(script: str, token_type: str) -> pynini.Fst:
 
 
 def MaybeLoadScriptConfig(
-    file_path: os.PathLike) -> script_config_pb2.ScriptConfig:
+    file_path: os.PathLike[str]) -> script_config_pb2.ScriptConfig:
   """Loads script configuration, if present."""
   pb = script_config_pb2.ScriptConfig()
   if not uf.IsFileExist(file_path):
diff --git a/nisaba/scripts/brahmic/visual_norm.py b/nisaba/scripts/brahmic/visual_norm.py
index b515711e..0a1fea4a 100644
--- a/nisaba/scripts/brahmic/visual_norm.py
+++ b/nisaba/scripts/brahmic/visual_norm.py
@@ -46,9 +46,9 @@
                                 'Token type: utf8 or byte')
 
 
-def core_visual_norm_fsts(rewrite_file: os.PathLike,
-                          preserve_file: os.PathLike,
-                          consonant_file: os.PathLike,
+def core_visual_norm_fsts(rewrite_file: os.PathLike[str],
+                          preserve_file: os.PathLike[str],
+                          consonant_file: os.PathLike[str],
                           sigma: pynini.Fst) -> List[pynini.Fst]:
   """Creates a visual normalization FST.
 
diff --git a/nisaba/scripts/brahmic/wellformed.py b/nisaba/scripts/brahmic/wellformed.py
index e58af465..ba104382 100644
--- a/nisaba/scripts/brahmic/wellformed.py
+++ b/nisaba/scripts/brahmic/wellformed.py
@@ -35,24 +35,24 @@
 import nisaba.scripts.utils.file as uf
 
 
-def _input_string_file(filename: os.PathLike,
+def _input_string_file(filename: os.PathLike[str],
                        return_if_empty: pynini.Fst = uf.EMPTY) -> pynini.Fst:
   fst = uf.StringFile(filename, return_if_empty)
   return pynini.project(fst, 'input').rmepsilon()
 
 
-def accept_well_formed(script_config_file: os.PathLike,
-                       consonant_file: os.PathLike,
-                       dead_consonant_file: os.PathLike,
-                       subjoined_consonant_file: os.PathLike,
-                       vowel_sign_file: os.PathLike,
-                       vowel_file: os.PathLike,
-                       vowel_length_sign_file: os.PathLike,
-                       coda_file: os.PathLike,
-                       standalone_file: os.PathLike,
-                       virama_file: os.PathLike,
-                       accept_file: os.PathLike,
-                       preserve_file: os.PathLike) -> pynini.Fst:
+def accept_well_formed(script_config_file: os.PathLike[str],
+                       consonant_file: os.PathLike[str],
+                       dead_consonant_file: os.PathLike[str],
+                       subjoined_consonant_file: os.PathLike[str],
+                       vowel_sign_file: os.PathLike[str],
+                       vowel_file: os.PathLike[str],
+                       vowel_length_sign_file: os.PathLike[str],
+                       coda_file: os.PathLike[str],
+                       standalone_file: os.PathLike[str],
+                       virama_file: os.PathLike[str],
+                       accept_file: os.PathLike[str],
+                       preserve_file: os.PathLike[str]) -> pynini.Fst:
   """Create an unweighted FSA to accept the well-formed strings in a script.
 
   Args:
diff --git a/nisaba/scripts/utils/char.py b/nisaba/scripts/utils/char.py
index 14978b8f..b22064bf 100644
--- a/nisaba/scripts/utils/char.py
+++ b/nisaba/scripts/utils/char.py
@@ -27,8 +27,9 @@
 ZWS = "\u200B"  # Zero Width Space
 
 
-def _read_string_file_chars_to_set(files: Iterable[os.PathLike],
-                                   relevant_fields: int) -> Set[str]:
+def _read_string_file_chars_to_set(
+    files: Iterable[os.PathLike[str]], relevant_fields: int
+) -> Set[str]:
   """Reads the characters under some selection from some file paths into a set.
 
   Arguments:
@@ -51,8 +52,10 @@ def _read_string_file_chars_to_set(files: Iterable[os.PathLike],
   return chars
 
 
-def derive_chars(both_sides: Iterable[os.PathLike] = (),
-                 input_side: Iterable[os.PathLike] = ()) -> Set[str]:
+def derive_chars(
+    both_sides: Iterable[os.PathLike[str]] = (),
+    input_side: Iterable[os.PathLike[str]] = ()
+) -> Set[str]:
   """Create the set of characters in a script from StringFiles.
 
   Args:
diff --git a/nisaba/scripts/utils/file.py b/nisaba/scripts/utils/file.py
index 6c437fe1..c95c5a6c 100644
--- a/nisaba/scripts/utils/file.py
+++ b/nisaba/scripts/utils/file.py
@@ -26,12 +26,12 @@
 EPSILON: pynini.Fst = pynini.accep("").optimize()
 
 
-def AsResourcePath(filename: os.PathLike) -> os.PathLike:
+def AsResourcePath(filename: os.PathLike[str]) -> os.PathLike[str]:
   filename = os.fspath(filename)
   return pathlib.Path(runfiles.Create().Rlocation(filename))
 
 
-def IsFileExist(filename: os.PathLike) -> bool:
+def IsFileExist(filename: os.PathLike[str]) -> bool:
   """Checks if a resource file exists."""
   try:
     if os.path.isfile(AsResourcePath(filename)):
@@ -47,7 +47,7 @@ def OnEmpty(fst, return_if_empty=EMPTY):
   return return_if_empty if fst.start() == pynini.NO_STATE_ID else fst
 
 
-def StringFile(filename: os.PathLike,
+def StringFile(filename: os.PathLike[str],
                return_if_empty: pynini.Fst = EMPTY) -> pynini.Fst:
   """Reads FST from `filename`. If FST is empty returns `return_if_empty`."""
   return OnEmpty(pynini.string_file(AsResourcePath(filename)), return_if_empty)
diff --git a/nisaba/scripts/utils/letter_languages.py b/nisaba/scripts/utils/letter_languages.py
index 5cc187d5..26d79744 100644
--- a/nisaba/scripts/utils/letter_languages.py
+++ b/nisaba/scripts/utils/letter_languages.py
@@ -41,7 +41,9 @@ def _fill_missing_raw(pb: ll.LetterLanguages) -> None:
     item.letter.raw, _ = us.convert_item(pb.uname_prefix, [], item.letter)
 
 
-def read_textproto(proto_path: Union[str, os.PathLike]) -> ll.LetterLanguages:
+def read_textproto(
+    proto_path: Union[str, os.PathLike[str]]
+) -> ll.LetterLanguages:
   pb = proto.read_textproto(proto_path, ll.LetterLanguages())
   _fill_missing_raw(pb)
   logging.info('Read %d letters.', len(pb.item))
diff --git a/nisaba/scripts/utils/proto.py b/nisaba/scripts/utils/proto.py
index cc047835..1745d655 100644
--- a/nisaba/scripts/utils/proto.py
+++ b/nisaba/scripts/utils/proto.py
@@ -29,7 +29,7 @@
 
 
 def read_textproto(
-    proto_path: Union[str, os.PathLike], proto: _ParsableT
+    proto_path: Union[str, os.PathLike[str]], proto: _ParsableT
 ) -> _ParsableT:
   logging.info('Parsing %s ...', proto_path)
   if not os.path.exists(proto_path):
diff --git a/nisaba/scripts/utils/rule.py b/nisaba/scripts/utils/rule.py
index 2b9af697..0bd87ddd 100644
--- a/nisaba/scripts/utils/rule.py
+++ b/nisaba/scripts/utils/rule.py
@@ -76,12 +76,12 @@
 RuleSets = List[RuleSet]
 
 
-def rules_from_string_file(file: os.PathLike) -> Iterator[Rule]:
+def rules_from_string_file(file: os.PathLike[str]) -> Iterator[Rule]:
   """Yields string rules from a text resource with unweighted string maps."""
   return rules_from_string_path(uf.AsResourcePath(file))
 
 
-def rules_from_string_path(file: os.PathLike) -> Iterator[Rule]:
+def rules_from_string_path(file: os.PathLike[str]) -> Iterator[Rule]:
   """Yields string rules from a text file with unweighted string maps."""
   with pathlib.Path(file).open('rt') as f:
     df = pd.read_csv(f, sep='\t', comment='#', escapechar='\\',
@@ -143,7 +143,9 @@ def fst_from_rules(rules: RuleSet, sigma: pynini.Fst) -> pynini.Fst:
   return ur.RewriteAndComposeFsts(fsts, sigma)
 
 
-def fst_from_rule_file(rule_file: os.PathLike, sigma: pynini.Fst) -> pynini.Fst:
+def fst_from_rule_file(
+    rule_file: os.PathLike[str], sigma: pynini.Fst
+) -> pynini.Fst:
   """Gets rewrite FST from a given rewrite rule file.
 
   Args:
@@ -172,7 +174,7 @@ def _fst_from_cascading_rules(rules: RuleSet, sigma: pynini.Fst) -> pynini.Fst:
   return ur.RewriteAndComposeFsts(fsts, sigma)
 
 
-def fst_from_cascading_rule_file(rule_file: os.PathLike,
+def fst_from_cascading_rule_file(rule_file: os.PathLike[str],
                                  sigma: pynini.Fst) -> pynini.Fst:
   """Gets rewrite FST from a given rewrite rule file.
 
diff --git a/nisaba/scripts/utils/unicode_strings_util.py b/nisaba/scripts/utils/unicode_strings_util.py
index a06faa8b..a242810f 100644
--- a/nisaba/scripts/utils/unicode_strings_util.py
+++ b/nisaba/scripts/utils/unicode_strings_util.py
@@ -168,7 +168,7 @@ def _fill_missing_raw(pb: unicode_strings_pb2.UnicodeStrings) -> None:
 
 
 def read_textproto(
-    proto_path: Union[str, os.PathLike],
+    proto_path: Union[str, os.PathLike[str]],
 ) -> unicode_strings_pb2.UnicodeStrings:
   pb = proto.read_textproto(proto_path, unicode_strings_pb2.UnicodeStrings())
   _fill_missing_raw(pb)