diff --git a/lib/python/pyflyby/_parse.py b/lib/python/pyflyby/_parse.py
index a566f11a..76fcacc9 100644
--- a/lib/python/pyflyby/_parse.py
+++ b/lib/python/pyflyby/_parse.py
@@ -353,7 +353,7 @@ def _annotate_ast_nodes(ast_node: ast.AST) -> AnnotatedAst:
 
 
 def _annotate_ast_startpos(
-    ast_node: ast.AST, parent_ast_node, minpos, text, flags
+    ast_node: ast.AST, parent_ast_node, minpos: FilePos, text: FileText, flags
 ) -> bool:
     r"""
     Annotate ``ast_node``.  Set ``ast_node.startpos`` to the starting position
@@ -410,8 +410,8 @@ def _annotate_ast_startpos(
     # Walk all nodes/fields of the AST.  We implement this as a custom
     # depth-first search instead of using ast.walk() or ast.NodeVisitor
     # so that we can easily keep track of the preceding node's lineno.
-    child_minpos = minpos
-    is_first_child = True
+    child_minpos: FilePos = minpos
+    is_first_child: bool = True
     leftstr_node = None
     for child_node in _iter_child_nodes_in_order(aast_node):
         leftstr = _annotate_ast_startpos(
@@ -954,8 +954,9 @@ def from_filename(cls, filename):
         return cls.from_text(Filename(filename))
 
     @classmethod
-    def from_text(cls, text, filename=None, startpos=None, flags=None,
-                  auto_flags=False):
+    def from_text(
+        cls, text, filename=None, startpos=None, flags=None, auto_flags: bool = False
+    ):
         """
         :type text:
           `FileText` or convertible
@@ -1153,7 +1154,7 @@ def expression_ast_node(self) -> Optional[ast.Expression]:
         else:
             return None
 
-    def parse(self, mode=None) -> Union[ast.Expression, ast.Module]:
+    def parse(self, mode: Optional[str] = None) -> Union[ast.Expression, ast.Module]:
         """
         Parse the source text into an AST.
 
@@ -1174,7 +1175,7 @@ def parse(self, mode=None) -> Union[ast.Expression, ast.Module]:
                 return self.expression_ast_node
             else:
                 raise SyntaxError
-        elif mode == None:
+        elif mode is None:
             if self.expression_ast_node:
                 return self.expression_ast_node
             else:
@@ -1185,7 +1186,7 @@ def parse(self, mode=None) -> Union[ast.Expression, ast.Module]:
         else:
             raise ValueError("parse(): invalid mode=%r" % (mode,))
 
-    def compile(self, mode=None):
+    def compile(self, mode: Optional[str] = None):
         """
         Parse into AST and compile AST into code.