diff --git a/CHANGES.md b/CHANGES.md
index d2955d2df0a..77fe17c03d3 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -43,6 +43,7 @@
 ### Performance
 
 <!-- Changes that improve Black's performance. -->
+- Speed up the `is_fstring_start` function in Black's tokenizer (#4541)
 
 ### Output
 
diff --git a/src/blib2to3/pgen2/tokenize.py b/src/blib2to3/pgen2/tokenize.py
index 97dd92b06f0..407c184dd74 100644
--- a/src/blib2to3/pgen2/tokenize.py
+++ b/src/blib2to3/pgen2/tokenize.py
@@ -221,7 +221,7 @@ def _combinations(*l: str) -> set[str]:
     | {f"{prefix}'" for prefix in _strprefixes | _fstring_prefixes}
     | {f'{prefix}"' for prefix in _strprefixes | _fstring_prefixes}
 )
-fstring_prefix: Final = (
+fstring_prefix: Final = tuple(
     {f"{prefix}'" for prefix in _fstring_prefixes}
     | {f'{prefix}"' for prefix in _fstring_prefixes}
     | {f"{prefix}'''" for prefix in _fstring_prefixes}
@@ -459,7 +459,7 @@ def untokenize(iterable: Iterable[TokenInfo]) -> str:
 
 
 def is_fstring_start(token: str) -> bool:
-    return builtins.any(token.startswith(prefix) for prefix in fstring_prefix)
+    return token.startswith(fstring_prefix)
 
 
 def _split_fstring_start_and_middle(token: str) -> tuple[str, str]: