diff --git a/blueprintcompiler/errors.py b/blueprintcompiler/errors.py
index 70aea2a..e3bc787 100644
--- a/blueprintcompiler/errors.py
+++ b/blueprintcompiler/errors.py
@@ -141,7 +141,7 @@ class CompilerBugError(Exception):
     """ Emitted on assertion errors """
 
 
-def assert_true(truth: bool, message:str=None):
+def assert_true(truth: bool, message: T.Optional[str]=None):
     if not truth:
         raise CompilerBugError(message)
 
diff --git a/blueprintcompiler/parse_tree.py b/blueprintcompiler/parse_tree.py
index bc36415..0e2644b 100644
--- a/blueprintcompiler/parse_tree.py
+++ b/blueprintcompiler/parse_tree.py
@@ -444,7 +444,7 @@ class Match(ParseNode):
         token = ctx.next_token()
         return str(token) == self.op
 
-    def expected(self, expect: str = None):
+    def expected(self, expect: T.Optional[str] = None):
         """ Convenience method for err(). """
         if expect is None:
             return self.err(f"Expected '{self.op}'")