diff --git a/crates/oxc_parser/src/diagnostics.rs b/crates/oxc_parser/src/diagnostics.rs
index 180bd0f5d02f1..47d6131f5059a 100644
--- a/crates/oxc_parser/src/diagnostics.rs
+++ b/crates/oxc_parser/src/diagnostics.rs
@@ -197,7 +197,7 @@ pub fn unterminated_string(span: Span) -> OxcDiagnostic {
 
 #[cold]
 pub fn reg_exp_flag(x0: char, span1: Span) -> OxcDiagnostic {
-    OxcDiagnostic::error(format!("Unexpected flag {x0} in regular expression literal"))
+    ts_error("1499", format!("Unexpected flag {x0} in regular expression literal"))
         .with_label(span1)
         .with_help(format!("The allowed flags are `{REGEXP_FLAGS_LIST}`"))
 }
diff --git a/tasks/coverage/snapshots/parser_test262.snap b/tasks/coverage/snapshots/parser_test262.snap
index 3e4dbadfd03e7..4f35e098a1989 100644
--- a/tasks/coverage/snapshots/parser_test262.snap
+++ b/tasks/coverage/snapshots/parser_test262.snap
@@ -23220,7 +23220,7 @@ Negative Passed: 4581/4581 (100.00%)
     ╰────
   help: Valid modifiers are: i, m, s
 
-  × Unexpected flag G in regular expression literal
+  × TS(1499): Unexpected flag G in regular expression literal
     ╭─[test262/test/language/literals/regexp/early-err-bad-flag.js:19:4]
  18 │ 
  19 │ /./G;
diff --git a/tasks/coverage/snapshots/parser_typescript.snap b/tasks/coverage/snapshots/parser_typescript.snap
index ff84556b1bc6f..3ce520af21f04 100644
--- a/tasks/coverage/snapshots/parser_typescript.snap
+++ b/tasks/coverage/snapshots/parser_typescript.snap
@@ -9993,7 +9993,7 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/statements/Va
    ╰────
   help: Valid group names are: foo
 
-  × Unexpected flag a in regular expression literal
+  × TS(1499): Unexpected flag a in regular expression literal
    ╭─[typescript/tests/cases/compiler/regularExpressionScanning.ts:3:11]
  2 │     // Flags
  3 │     /foo/visualstudiocode,
@@ -10002,7 +10002,7 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/statements/Va
    ╰────
   help: The allowed flags are `gimsuydv`
 
-  × Unexpected flag l in regular expression literal
+  × TS(1499): Unexpected flag l in regular expression literal
    ╭─[typescript/tests/cases/compiler/regularExpressionScanning.ts:3:12]
  2 │     // Flags
  3 │     /foo/visualstudiocode,
@@ -10020,7 +10020,7 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/statements/Va
    ╰────
   help: Remove the duplicated flag here
 
-  × Unexpected flag t in regular expression literal
+  × TS(1499): Unexpected flag t in regular expression literal
    ╭─[typescript/tests/cases/compiler/regularExpressionScanning.ts:3:14]
  2 │     // Flags
  3 │     /foo/visualstudiocode,
@@ -10047,7 +10047,7 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/statements/Va
    ╰────
   help: Remove the duplicated flag here
 
-  × Unexpected flag o in regular expression literal
+  × TS(1499): Unexpected flag o in regular expression literal
    ╭─[typescript/tests/cases/compiler/regularExpressionScanning.ts:3:18]
  2 │     // Flags
  3 │     /foo/visualstudiocode,
@@ -10056,7 +10056,7 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/statements/Va
    ╰────
   help: The allowed flags are `gimsuydv`
 
-  × Unexpected flag c in regular expression literal
+  × TS(1499): Unexpected flag c in regular expression literal
    ╭─[typescript/tests/cases/compiler/regularExpressionScanning.ts:3:19]
  2 │     // Flags
  3 │     /foo/visualstudiocode,
@@ -10065,7 +10065,7 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/statements/Va
    ╰────
   help: The allowed flags are `gimsuydv`
 
-  × Unexpected flag o in regular expression literal
+  × TS(1499): Unexpected flag o in regular expression literal
    ╭─[typescript/tests/cases/compiler/regularExpressionScanning.ts:3:20]
  2 │     // Flags
  3 │     /foo/visualstudiocode,
@@ -10083,7 +10083,7 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/statements/Va
    ╰────
   help: Remove the duplicated flag here
 
-  × Unexpected flag e in regular expression literal
+  × TS(1499): Unexpected flag e in regular expression literal
    ╭─[typescript/tests/cases/compiler/regularExpressionScanning.ts:3:22]
  2 │     // Flags
  3 │     /foo/visualstudiocode,
@@ -23009,7 +23009,7 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/statements/Va
    ╰────
   help: Try inserting a semicolon here
 
-  × Unexpected flag a in regular expression literal
+  × TS(1499): Unexpected flag a in regular expression literal
    ╭─[typescript/tests/cases/conformance/parser/ecmascript5/RegularExpressions/parserRegularExpressionDivideAmbiguity3.ts:1:16]
  1 │ if (1) /regexp/a.foo();
    ·                ─