diff --git a/CHANGES.md b/CHANGES.md
index b39f9ab4f54..79e7b0b1444 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -30,6 +30,8 @@
 
 <!-- Changes that improve Black's performance. -->
 
+- Fix bad performance on certain complex string literals (#4331)
+
 ### Output
 
 <!-- Changes to Black's terminal output and error messages -->
diff --git a/src/blib2to3/pgen2/tokenize.py b/src/blib2to3/pgen2/tokenize.py
index d6b684ab1aa..fd0b5564f43 100644
--- a/src/blib2to3/pgen2/tokenize.py
+++ b/src/blib2to3/pgen2/tokenize.py
@@ -119,13 +119,13 @@ def _combinations(*l: str) -> Set[str]:
 Number = group(Imagnumber, Floatnumber, Intnumber)
 
 # Tail end of ' string.
-Single = r"[^'\\]*(?:\\.[^'\\]*)*'"
+Single = r"(?:\\.|[^'\\])*'"
 # Tail end of " string.
-Double = r'[^"\\]*(?:\\.[^"\\]*)*"'
+Double = r'(?:\\.|[^"\\])*"'
 # Tail end of ''' string.
-Single3 = r"[^'\\]*(?:(?:\\.|'(?!''))[^'\\]*)*'''"
+Single3 = r"(?:\\.|'(?!'')|[^'\\])*'''"
 # Tail end of """ string.
-Double3 = r'[^"\\]*(?:(?:\\.|"(?!""))[^"\\]*)*"""'
+Double3 = r'(?:\\.|"(?!"")|[^"\\])*"""'
 _litprefix = r"(?:[uUrRbB]|[rR][bB]|[bBuU][rR])?"
 _fstringlitprefix = r"(?:rF|FR|Fr|fr|RF|F|rf|f|Rf|fR)"
 Triple = group(
@@ -136,12 +136,12 @@ def _combinations(*l: str) -> Set[str]:
 )
 
 # beginning of a single quoted f-string. must not end with `{{` or `\N{`
-SingleLbrace = r"[^'\\{]*(?:(?:\\N{|\\.|{{)[^'\\{]*)*(?<!\\N){(?!{)"
-DoubleLbrace = r'[^"\\{]*(?:(?:\\N{|\\.|{{)[^"\\{]*)*(?<!\\N){(?!{)'
+SingleLbrace = r"(?:\\N{|\\.|{{|[^'\\{])*(?<!\\N){(?!{)"
+DoubleLbrace = r'(?:\\N{|\\.|{{|[^"\\{])*(?<!\\N){(?!{)'
 
 # beginning of a triple quoted f-string. must not end with `{{` or `\N{`
-Single3Lbrace = r"[^'{]*(?:(?:\\N{|\\[^{]|{{|'(?!''))[^'{]*)*(?<!\\N){(?!{)"
-Double3Lbrace = r'[^"{]*(?:(?:\\N{|\\[^{]|{{|"(?!""))[^"{]*)*(?<!\\N){(?!{)'
+Single3Lbrace = r"(?:\\N{|\\[^{]|{{|'(?!'')|[^'{\\])*(?<!\\N){(?!{)"
+Double3Lbrace = r'(?:\\N{|\\[^{]|{{|"(?!"")|[^"{\\])*(?<!\\N){(?!{)'
 
 # ! format specifier inside an fstring brace, ensure it's not a `!=` token
 Bang = Whitespace + group("!") + r"(?!=)"
@@ -171,12 +171,12 @@ def _combinations(*l: str) -> Set[str]:
 Special = group(r"\r?\n", r"[:;.,`@]")
 Funny = group(Operator, Bracket, Special)
 
-_string_middle_single = r"[^\n'\\]*(?:\\.[^\n'\\]*)*"
-_string_middle_double = r'[^\n"\\]*(?:\\.[^\n"\\]*)*'
+_string_middle_single = r"(?:[^\n'\\]|\\.)*"
+_string_middle_double = r'(?:[^\n"\\]|\\.)*'
 
 # FSTRING_MIDDLE and LBRACE, must not end with a `{{` or `\N{`
-_fstring_middle_single = r"[^\n'{]*(?:(?:\\N{|\\[^{]|{{)[^\n'{]*)*(?<!\\N)({)(?!{)"
-_fstring_middle_double = r'[^\n"{]*(?:(?:\\N{|\\[^{]|{{)[^\n"{]*)*(?<!\\N)({)(?!{)'
+_fstring_middle_single = r"(?:\\N{|\\[^{]|{{|[^\n'{\\])*(?<!\\N)({)(?!{)"
+_fstring_middle_double = r'(?:\\N{|\\[^{]|{{|[^\n"{\\])*(?<!\\N)({)(?!{)'
 
 # First (or only) line of ' or " string.
 ContStr = group(
diff --git a/tests/data/cases/pep_701.py b/tests/data/cases/pep_701.py
index f4a69e47413..a0b67413ee9 100644
--- a/tests/data/cases/pep_701.py
+++ b/tests/data/cases/pep_701.py
@@ -119,6 +119,8 @@
     level=0,
 )
 
+f'{{\\"kind\\":\\"ConfigMap\\",\\"metadata\\":{{\\"annotations\\":{{}},\\"name\\":\\"cluster-info\\",\\"namespace\\":\\"amazon-cloudwatch\\"}}}}'
+
 # output
 
 x = f"foo"
@@ -240,3 +242,5 @@
     f"{self.writer._transport.get_extra_info('peername')}",  # type: ignore[attr-defined]
     level=0,
 )
+
+f'{{\\"kind\\":\\"ConfigMap\\",\\"metadata\\":{{\\"annotations\\":{{}},\\"name\\":\\"cluster-info\\",\\"namespace\\":\\"amazon-cloudwatch\\"}}}}'