diff --git a/crates/ruff_python_parser/src/parser/expression.rs b/crates/ruff_python_parser/src/parser/expression.rs
index 50581346cc90f5..122b21305adc99 100644
--- a/crates/ruff_python_parser/src/parser/expression.rs
+++ b/crates/ruff_python_parser/src/parser/expression.rs
@@ -2,6 +2,7 @@ use std::ops::Deref;
 
 use bitflags::bitflags;
 use rustc_hash::{FxBuildHasher, FxHashSet};
+use thin_vec::ThinVec;
 
 use ruff_python_ast::name::Name;
 use ruff_python_ast::token::TokenKind;
@@ -806,7 +807,7 @@ impl<'src> Parser<'src> {
         self.bump(TokenKind::Lpar);
 
         let mut args = vec![];
-        let mut keywords = vec![];
+        let mut keywords = ThinVec::new();
         let mut seen_keyword_argument = false; // foo = 1
         let mut seen_keyword_unpacking = false; // **foo
 
@@ -933,11 +934,13 @@ impl<'src> Parser<'src> {
 
         self.expect(TokenKind::Rpar);
 
+        keywords.shrink_to_fit();
+
         let arguments = ast::Arguments {
             range: self.node_range(start),
             node_index: AtomicNodeIndex::NONE,
             args: args.into_boxed_slice(),
-            keywords: keywords.into(),
+            keywords,
         };
 
         self.validate_arguments(&arguments, has_trailing_comma, context);