diff --git a/native/libcst/src/parser/grammar.rs b/native/libcst/src/parser/grammar.rs
index 14622c1a9..5e23357d3 100644
--- a/native/libcst/src/parser/grammar.rs
+++ b/native/libcst/src/parser/grammar.rs
@@ -1004,7 +1004,7 @@ parser! {
                     make_slice(l, col, u, rest)
             }
             / e:starred_expression() { make_index_from_arg(e) }
-            / v:expression() { make_index(v) }
+            / v:named_expression() { make_index(v) }
 
         rule atom() -> Expression<'input, 'a>
             = n:name() { Expression::Name(Box::new(n)) }
diff --git a/native/libcst/src/tokenizer/core/mod.rs b/native/libcst/src/tokenizer/core/mod.rs
index 7c0f0788e..d470a78a7 100644
--- a/native/libcst/src/tokenizer/core/mod.rs
+++ b/native/libcst/src/tokenizer/core/mod.rs
@@ -114,12 +114,8 @@ pub enum TokType {
     Dedent,
     Async,
     Await,
-    // TODO; add support for these
-    #[allow(dead_code)]
     FStringStart,
-    #[allow(dead_code)]
     FStringString,
-    #[allow(dead_code)]
     FStringEnd,
     EndMarker,
 }
diff --git a/native/libcst/src/tokenizer/core/string_types.rs b/native/libcst/src/tokenizer/core/string_types.rs
index 8f9e0cf0f..d14d13f5b 100644
--- a/native/libcst/src/tokenizer/core/string_types.rs
+++ b/native/libcst/src/tokenizer/core/string_types.rs
@@ -98,11 +98,10 @@ impl FStringNode {
     }
 
     pub fn close_parentheses(&mut self) {
-        self.parentheses_count -= 1;
-        if self.parentheses_count == 0 {
-            // No parentheses means that the format spec is also finished.
-            self.format_spec_count = 0;
+        if self.is_in_format_spec() {
+            self.format_spec_count -= 1;
         }
+        self.parentheses_count -= 1;
     }
 
     pub fn allow_multiline(&self) -> bool {
diff --git a/native/libcst/src/tokenizer/tests.rs b/native/libcst/src/tokenizer/tests.rs
index 4e8ce4d3e..08d26e555 100644
--- a/native/libcst/src/tokenizer/tests.rs
+++ b/native/libcst/src/tokenizer/tests.rs
@@ -814,3 +814,29 @@ fn test_inconsistent_indentation_at_eof() {
         ])
     )
 }
+
+#[test]
+fn test_nested_f_string_specs() {
+    let config = TokConfig {
+        split_fstring: true,
+        ..default_config()
+    };
+    assert_eq!(
+        tokenize_all("f'{_:{_:}{_}}'", &config),
+        Ok(vec![
+            (TokType::FStringStart, "f'"),
+            (TokType::Op, "{"),
+            (TokType::Name, "_"),
+            (TokType::Op, ":"),
+            (TokType::Op, "{"),
+            (TokType::Name, "_"),
+            (TokType::Op, ":"),
+            (TokType::Op, "}"),
+            (TokType::Op, "{"),
+            (TokType::Name, "_"),
+            (TokType::Op, "}"),
+            (TokType::Op, "}"),
+            (TokType::FStringEnd, "'")
+        ])
+    )
+}
diff --git a/native/libcst/tests/fixtures/super_strings.py b/native/libcst/tests/fixtures/super_strings.py
index d993f5abd..824572793 100644
--- a/native/libcst/tests/fixtures/super_strings.py
+++ b/native/libcst/tests/fixtures/super_strings.py
@@ -30,3 +30,5 @@
 f'\{{\}}'
 f"regexp_like(path, '.*\{file_type}$')"
 f"\lfoo"
+
+f"{_:{_:}{a}}"
\ No newline at end of file
diff --git a/native/libcst/tests/fixtures/wonky_walrus.py b/native/libcst/tests/fixtures/wonky_walrus.py
index d0916ab80..d506b169b 100644
--- a/native/libcst/tests/fixtures/wonky_walrus.py
+++ b/native/libcst/tests/fixtures/wonky_walrus.py
@@ -10,4 +10,6 @@
 if f := x(): pass
 
 f(y:=1)
-f(x,  y   :=    1     )
\ No newline at end of file
+f(x,  y   :=    1     )
+
+_[_:=10]
\ No newline at end of file