diff --git a/rewrite/rewrite/python/_parser_visitor.py b/rewrite/rewrite/python/_parser_visitor.py
index 248dd20..df07910 100644
--- a/rewrite/rewrite/python/_parser_visitor.py
+++ b/rewrite/rewrite/python/_parser_visitor.py
@@ -3,8 +3,7 @@
 from functools import lru_cache
 from io import BytesIO
 from pathlib import Path
-from random import random
-from tokenize import tokenize
+from tokenize import tokenize, TokenInfo
 from typing import Optional, TypeVar, cast, Callable, List, Tuple, Dict, Type, Sequence
 
 from rewrite import random_id, Markers
@@ -974,7 +973,7 @@ def _map_comprehension_condition(self, i):
         )
 
     def visit_Module(self, node: ast.Module) -> py.CompilationUnit:
-        return py.CompilationUnit(
+        cu = py.CompilationUnit(
             random_id(),
             Space.EMPTY,
             Markers.EMPTY,
@@ -988,6 +987,8 @@ def visit_Module(self, node: ast.Module) -> py.CompilationUnit:
                 self.__pad_right(j.Empty(random_id(), Space.EMPTY, Markers.EMPTY), Space.EMPTY)],
             self.__whitespace()
         )
+        # assert self._cursor == len(self._source)
+        return cu
 
     def visit_Name(self, node):
         return j.Identifier(
@@ -1350,8 +1351,7 @@ def _map_assignment_operator(self, op):
             raise ValueError(f"Unsupported operator: {op}")
         return self.__pad_left(self.__source_before(op_str), op)
 
-    def __map_fstring(self, node, prefix, tok, tokens):
-        consume_end_delim = False
+    def __map_fstring(self, node: ast.JoinedStr, prefix: Space, tok: TokenInfo, tokens):
         if tok.type != token.FSTRING_START:
             if len(node.values) == 1 and isinstance(node.values[0], ast.Constant):
                 # format specifiers are stored as f-strings in the AST; e.g. `f'{1:n}'`
@@ -1368,6 +1368,7 @@ def __map_fstring(self, node, prefix, tok, tokens):
                 ), next(tokens))
             else:
                 delimiter = ''
+            consume_end_delim = False
         else:
             delimiter = tok.string
             self._cursor += len(delimiter)
@@ -1377,10 +1378,11 @@ def __map_fstring(self, node, prefix, tok, tokens):
         # tokenizer tokens: FSTRING_START, FSTRING_MIDDLE, OP, ..., OP, FSTRING_MIDDLE, FSTRING_END
         parts = []
         for value in node.values:
-            if tok.type == token.OP:
+            if tok.type == token.OP and tok.string == '{':
                 self._cursor += len(tok.string)
-                if isinstance(value.value, ast.JoinedStr):
-                    nested, tok = self.__map_fstring(value.value, Space.EMPTY, next(tokens), tokens)
+                tok = next(tokens)
+                if isinstance(cast(ast.FormattedValue, value).value, ast.JoinedStr):
+                    nested, tok = self.__map_fstring(cast(ast.JoinedStr, cast(ast.FormattedValue, value).value), Space.EMPTY, tok, tokens)
                     expr = self.__pad_right(
                         nested,
                         Space.EMPTY
@@ -1390,7 +1392,7 @@ def __map_fstring(self, node, prefix, tok, tokens):
                     tok = next(tokens)
                 else:
                     expr = self.__pad_right(
-                        self.__convert(value.value),
+                        self.__convert(cast(ast.FormattedValue, value).value),
                         self.__whitespace()
                     )
                     prev_tok = tok