diff --git a/crates/oxc_parser/src/diagnostics.rs b/crates/oxc_parser/src/diagnostics.rs
index 7a1ce56761087..05d93172ba936 100644
--- a/crates/oxc_parser/src/diagnostics.rs
+++ b/crates/oxc_parser/src/diagnostics.rs
@@ -504,10 +504,17 @@ pub fn modifier_cannot_be_used_here(modifier: &Modifier) -> OxcDiagnostic {
         .with_label(modifier.span)
 }
 
+/// TS(1028)
+#[cold]
+pub fn accessibility_modifier_already_seen(modifier: &Modifier) -> OxcDiagnostic {
+    ts_error("1028", "Accessibility modifier already seen.")
+        .with_label(modifier.span)
+        .with_help("Remove the duplicate modifier.")
+}
+
 /// TS(1030)
 #[cold]
 pub fn modifier_already_seen(modifier: &Modifier) -> OxcDiagnostic {
-    // OxcDiagnostic::error(format!("TS1030: '{}' modifier already seen.", modifier.kind))
     ts_error("1030", format!("{}' modifier already seen.", modifier.kind))
         .with_label(modifier.span)
         .with_help("Remove the duplicate modifier.")
diff --git a/crates/oxc_parser/src/ts/types.rs b/crates/oxc_parser/src/ts/types.rs
index 3f3e7eb547904..99eba60233fee 100644
--- a/crates/oxc_parser/src/ts/types.rs
+++ b/crates/oxc_parser/src/ts/types.rs
@@ -1328,8 +1328,13 @@ impl<'a> ParserImpl<'a> {
 
             if let Ok(kind) = ModifierKind::try_from(self.cur_kind()) {
                 let modifier = Modifier { kind, span: self.cur_token().span() };
-                flags.set(kind.into(), true);
-                modifiers.push(modifier);
+                let new_flag = ModifierFlags::from(kind);
+                if flags.contains(new_flag) {
+                    self.error(diagnostics::accessibility_modifier_already_seen(&modifier));
+                } else {
+                    flags.insert(new_flag);
+                    modifiers.push(modifier);
+                }
             } else {
                 break;
             }
diff --git a/tasks/coverage/snapshots/parser_typescript.snap b/tasks/coverage/snapshots/parser_typescript.snap
index c8be9aa211ed0..0794909111b11 100644
--- a/tasks/coverage/snapshots/parser_typescript.snap
+++ b/tasks/coverage/snapshots/parser_typescript.snap
@@ -3,7 +3,7 @@ commit: 15392346
 parser_typescript Summary:
 AST Parsed     : 6522/6531 (99.86%)
 Positive Passed: 6511/6531 (99.69%)
-Negative Passed: 1287/5754 (22.37%)
+Negative Passed: 1288/5754 (22.38%)
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/compiler/ClassDeclaration24.ts
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/compiler/ExportAssignment7.ts
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/compiler/ExportAssignment8.ts
@@ -409,7 +409,6 @@ Expect Syntax Error: tasks/coverage/typescript/tests/cases/compiler/constantEnum
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/compiler/constraintErrors1.ts
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/compiler/constraintWithIndexedAccess.ts
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/compiler/constraints0.ts
-Expect Syntax Error: tasks/coverage/typescript/tests/cases/compiler/constructorArgsErrors3.ts
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/compiler/constructorArgsErrors4.ts
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/compiler/constructorAsType.ts
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/compiler/constructorInvocationWithTooFewTypeArgs.ts
@@ -6965,6 +6964,15 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/salsa/private
  3 │     }
    ╰────
 
+  × TS(1028): Accessibility modifier already seen.
+   ╭─[typescript/tests/cases/compiler/constructorArgsErrors3.ts:2:25]
+ 1 │ class foo {
+ 2 │     constructor (public public a: number) {
+   ·                         ──────
+ 3 │     }
+   ╰────
+  help: Remove the duplicate modifier.
+
   × TS(1090): 'export' modifier cannot appear on a parameter.
    ╭─[typescript/tests/cases/compiler/constructorArgsErrors5.ts:2:18]
  1 │ class foo {
@@ -14664,6 +14672,15 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/salsa/private
    ╰────
   help: Remove the duplicate modifier.
 
+  × TS(1028): Accessibility modifier already seen.
+   ╭─[typescript/tests/cases/conformance/classes/constructorDeclarations/constructorParameters/readonlyReadonly.ts:3:26]
+ 2 │     readonly readonly x: number;
+ 3 │     constructor(readonly readonly y: number) {}
+   ·                          ────────
+ 4 │ }
+   ╰────
+  help: Remove the duplicate modifier.
+
   × Super calls are not permitted outside constructors or in nested functions inside constructors.
     ╭─[typescript/tests/cases/conformance/classes/constructorDeclarations/superCalls/derivedClassConstructorWithoutSuperCall.ts:24:31]
  23 │     constructor() { // error