diff --git a/CHANGELOG.md b/CHANGELOG.md
index cb43b0c..6dbee8a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,9 +6,12 @@ All notable changes to this project will be documented in this file.
 
 <!-- unreleased things below this line -->
 
+* Refactor
+  * Marked exported constants/lazy globals as `Final` for downstream users (via [#69])
 * Docs
   * Fixed docstring of `T_SYNTAX_PARSER_TERM` (via [#70]) 
 
+[#69]: https://github.com/jkowalleck/rfc3987-syntax2/pull/69
 [#70]: https://github.com/jkowalleck/rfc3987-syntax2/pull/70
 
 ## v1.3.1 - 2026-07-23
diff --git a/src/rfc3987_syntax2/syntax_helpers.py b/src/rfc3987_syntax2/syntax_helpers.py
index 57790e2..689e073 100644
--- a/src/rfc3987_syntax2/syntax_helpers.py
+++ b/src/rfc3987_syntax2/syntax_helpers.py
@@ -4,7 +4,7 @@
 
 from pathlib import Path
 from threading import Lock
-from typing import TYPE_CHECKING, Any, Callable, Literal, Optional
+from typing import TYPE_CHECKING, Any, Callable, Final, Literal, Mapping, Optional, Sequence
 from warnings import warn
 
 from lark import Lark, ParseTree, exceptions
@@ -65,9 +65,9 @@
     "is_valid_syntax_pct_encoded",
 ]
 
-RFC3987_SYNTAX_PARSER_TYPE: str = "earley"
-RFC3987_SYNTAX_GRAMMAR_PATH: Path = Path(__file__).parent / "syntax_rfc3987.lark"
-RFC3987_SYNTAX_TERMS: list[str] = [
+RFC3987_SYNTAX_PARSER_TYPE: Final[str] = "earley"
+RFC3987_SYNTAX_GRAMMAR_PATH: Final[Path] = Path(__file__).parent / "syntax_rfc3987.lark"
+RFC3987_SYNTAX_TERMS: Final[Sequence[str]] = [  # TODO: BreakingChaneg: make tuple
     "iri",
     "iri_reference",
     "absolute_iri",
@@ -124,7 +124,7 @@
 Allowed values are ``"iri"``, ``"iri_reference"``, and ``"absolute_iri"``.
 """
 
-_SYNTAX_PARSER_STARTS: list[T_SYNTAX_PARSER_TERM] = ["iri", "iri_reference", "absolute_iri"]
+_SYNTAX_PARSER_STARTS: Final[Sequence[T_SYNTAX_PARSER_TERM]] = ["iri", "iri_reference", "absolute_iri"]
 
 
 def parse(term: T_SYNTAX_PARSER_TERM, value: str) -> ParseTree:
@@ -161,6 +161,7 @@ def is_valid_syntax(term: T_SYNTAX_PARSER_TERM, value: str) -> bool:
         return False
     except exceptions.LarkError as err:
         # from Lark internals / initialization (non-UnexpectedInput)
+        # TODO: BreakingChange: dont catch
         warn("Unexpected LarkError (non-UnexpectedInput) "
              f"for term={term!r}: {type(err).__name__}: {err}",
              RuntimeWarning,
@@ -526,7 +527,8 @@ def is_valid_syntax_pct_encoded(text: str) -> bool:
     is_valid_syntax_pct_encoded = make_syntax_validator("pct_encoded")
 
 
-RFC3987_SYNTAX_TERM_VALIDATORS: dict[str, T_SYNTAX_VALIDATOR] = {  # frozendict
+RFC3987_SYNTAX_TERM_VALIDATORS: Final[Mapping[str, T_SYNTAX_VALIDATOR]] = {
+    # TODO: BreakingChange: make frozendict / MappingProxyType
     "iri": is_valid_syntax_iri,
     "iri_reference": is_valid_syntax_iri_reference,
     "absolute_iri": is_valid_syntax_absolute_iri,
@@ -578,22 +580,22 @@ def is_valid_syntax_pct_encoded(text: str) -> bool:
 # region lazy loaded attrs
 
 if TYPE_CHECKING:  # types for lazy-loaded symbols
-    grammar: str
+    grammar: Final[str]  # type: ignore[misc]  # lazy loading is Final downstream
     """Lark grammar text for RFC 3987."""
 
 if TYPE_CHECKING:  # types for lazy-loaded symbols
-    syntax_parser: Lark
+    syntax_parser: Final[Lark]  # type: ignore[misc]  # lazy loading is Final downstream
     """Lazily initialized parser for RFC 3987 syntax."""
 
 
 def __getattr__(name: str) -> Any:
     if name == "grammar":
         global grammar
-        grammar = _get_grammar()
+        grammar = _get_grammar()  # type: ignore[misc]  # lazy loading is Final downstream
         return grammar
     if name == "syntax_parser":
         global syntax_parser
-        syntax_parser = _get_syntax_parser()
+        syntax_parser = _get_syntax_parser()  # type: ignore[misc]  # lazy loading is Final downstream
         return syntax_parser
     raise AttributeError(f"module {__name__!r} has no attribute {name!r}")