diff --git a/crates/oxc_ast/src/ast/literal.rs b/crates/oxc_ast/src/ast/literal.rs
index 39310b5b5ede2..8e8c06de915cc 100644
--- a/crates/oxc_ast/src/ast/literal.rs
+++ b/crates/oxc_ast/src/ast/literal.rs
@@ -5,6 +5,7 @@ use std::{
     hash::{Hash, Hasher},
 };
 
+use bitflags::bitflags;
 use num_bigint::BigUint;
 use ordered_float::NotNan;
 use serde::{
@@ -110,7 +111,7 @@ pub struct RegExpLiteral {
 #[derive(Debug, Clone, Serialize, PartialEq, Eq, Hash)]
 pub struct RegExp {
     pub pattern: Atom,
-    pub flags: Atom,
+    pub flags: RegExpFlags,
 }
 
 impl fmt::Display for RegExp {
@@ -119,6 +120,59 @@ impl fmt::Display for RegExp {
     }
 }
 
+bitflags! {
+    pub struct RegExpFlags: u8 {
+        const G = 1 << 0;
+        const I = 1 << 1;
+        const M = 1 << 2;
+        const S = 1 << 3;
+        const U = 1 << 4;
+        const Y = 1 << 5;
+        const D = 1 << 6;
+        /// v flag from `https://github.com/tc39/proposal-regexp-set-notation`
+        const V = 1 << 7;
+    }
+}
+
+impl fmt::Display for RegExpFlags {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        if self.contains(Self::G) {
+            write!(f, "g")?;
+        }
+        if self.contains(Self::I) {
+            write!(f, "i")?;
+        }
+        if self.contains(Self::M) {
+            write!(f, "m")?;
+        }
+        if self.contains(Self::S) {
+            write!(f, "s")?;
+        }
+        if self.contains(Self::U) {
+            write!(f, "u")?;
+        }
+        if self.contains(Self::Y) {
+            write!(f, "y")?;
+        }
+        if self.contains(Self::D) {
+            write!(f, "d")?;
+        }
+        if self.contains(Self::V) {
+            write!(f, "v")?;
+        }
+        Ok(())
+    }
+}
+
+impl Serialize for RegExpFlags {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        serializer.serialize_str(&self.to_string())
+    }
+}
+
 #[derive(Debug, Clone, Serialize, PartialEq, Eq, Hash)]
 pub struct EmptyObject {}
 
diff --git a/crates/oxc_parser/src/lexer/mod.rs b/crates/oxc_parser/src/lexer/mod.rs
index 497a0988c4fbe..cdb50a12fda21 100644
--- a/crates/oxc_parser/src/lexer/mod.rs
+++ b/crates/oxc_parser/src/lexer/mod.rs
@@ -21,7 +21,7 @@ use constants::{
 pub use kind::Kind;
 use number::{parse_big_int, parse_float, parse_int};
 use oxc_allocator::{Allocator, String};
-use oxc_ast::{Atom, Node, SourceType};
+use oxc_ast::{ast::RegExpFlags, Atom, Node, SourceType};
 use oxc_diagnostics::{Diagnostic, Diagnostics};
 use simd::{SkipMultilineComment, SkipWhitespace};
 use string_builder::AutoCow;
@@ -1010,35 +1010,39 @@ impl<'a> Lexer<'a> {
 
         pattern.push_str(&start[..start.len() - self.current.chars.as_str().len() - 1]);
 
-        let mut flags = String::new_in(self.allocator);
-        while let c @ ('$' | '_' | 'a'..='z' | 'A'..='Z' | '0'..='9') = self.peek() {
-            self.current.chars.next();
-            flags.push(c);
-        }
+        let mut flags = RegExpFlags::empty();
 
-        // v flag from https://github.com/tc39/proposal-regexp-set-notation
-        let gimsuy_mask: u32 =
-            ['g', 'i', 'm', 's', 'u', 'y', 'd', 'v'].iter().map(|x| 1 << ((*x as u8) - b'a')).sum();
-        let mut flag_text_set: u32 = 0;
-        for ch in flags.chars() {
+        while let ch @ ('$' | '_' | 'a'..='z' | 'A'..='Z' | '0'..='9') = self.peek() {
+            self.current.chars.next();
+            // dbg!(ch);
             if !ch.is_ascii_lowercase() {
                 self.error(Diagnostic::RegExpFlag(ch, self.current_offset()));
                 continue;
             }
-            let ch_mask = 1 << ((ch as u8) - b'a');
-            if ch_mask & gimsuy_mask == 0 {
-                self.error(Diagnostic::RegExpFlag(ch, self.current_offset()));
-            }
-            if flag_text_set & ch_mask != 0 {
+            let flag = match ch {
+                'g' => RegExpFlags::G,
+                'i' => RegExpFlags::I,
+                'm' => RegExpFlags::M,
+                's' => RegExpFlags::S,
+                'u' => RegExpFlags::U,
+                'y' => RegExpFlags::Y,
+                'd' => RegExpFlags::D,
+                'v' => RegExpFlags::V,
+                _ => {
+                    self.error(Diagnostic::RegExpFlag(ch, self.current_offset()));
+                    continue;
+                }
+            };
+            if flags.contains(flag) {
                 self.error(Diagnostic::RegExpFlagTwice(ch, self.current_offset()));
+                continue;
             }
-            flag_text_set |= ch_mask;
+            flags |= flag;
         }
 
-        self.current.token.value = TokenValue::RegExp(RegExp {
-            pattern: Atom::from(pattern.as_str()),
-            flags: Atom::from(flags.as_str()),
-        });
+        self.current.token.value =
+            TokenValue::RegExp(RegExp { pattern: Atom::from(pattern.as_str()), flags });
+
         Kind::RegExp
     }
 
diff --git a/crates/oxc_parser/src/lexer/token.rs b/crates/oxc_parser/src/lexer/token.rs
index 5ec9bcb6ae38b..16f7fae5b2841 100644
--- a/crates/oxc_parser/src/lexer/token.rs
+++ b/crates/oxc_parser/src/lexer/token.rs
@@ -1,7 +1,7 @@
 //! Token
 
 use num_bigint::BigUint;
-use oxc_ast::{Atom, Node};
+use oxc_ast::{ast::RegExpFlags, Atom, Node};
 
 use super::kind::Kind;
 
@@ -25,6 +25,13 @@ pub struct Token {
     pub value: TokenValue,
 }
 
+#[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
+#[test]
+fn no_bloat_token() {
+    use std::mem::size_of;
+    assert_eq!(size_of::<Token>(), 56);
+}
+
 impl Token {
     #[must_use]
     pub const fn node(&self) -> Node {
@@ -44,7 +51,7 @@ pub enum TokenValue {
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct RegExp {
     pub pattern: Atom,
-    pub flags: Atom,
+    pub flags: RegExpFlags,
 }
 
 impl Default for TokenValue {
diff --git a/crates/oxc_printer/src/gen.rs b/crates/oxc_printer/src/gen.rs
index f386899effd3f..eae1e7021a70c 100644
--- a/crates/oxc_printer/src/gen.rs
+++ b/crates/oxc_printer/src/gen.rs
@@ -841,7 +841,7 @@ impl Gen for RegExpLiteral {
         p.print(b'/');
         p.print_str(self.regex.pattern.as_bytes());
         p.print(b'/');
-        p.print_str(self.regex.flags.as_bytes());
+        p.print_str(self.regex.flags.to_string().as_bytes());
     }
 }