diff --git a/boa/src/syntax/parser/function/mod.rs b/boa/src/syntax/parser/function/mod.rs
index ee3463cef3..abc2f780cc 100644
--- a/boa/src/syntax/parser/function/mod.rs
+++ b/boa/src/syntax/parser/function/mod.rs
@@ -12,10 +12,7 @@ mod tests;
 
 use crate::{
     syntax::{
-        ast::{
-            node::{self},
-            Punctuator,
-        },
+        ast::{node, Punctuator},
         lexer::{InputElement, TokenKind},
         parser::{
             expression::Initializer,
@@ -25,7 +22,7 @@ use crate::{
     },
     BoaProfiler,
 };
-use std::io::Read;
+use std::{collections::HashSet, io::Read};
 
 /// Formal parameters parsing.
 ///
@@ -66,6 +63,7 @@ where
         cursor.set_goal(InputElement::RegExp);
 
         let mut params = Vec::new();
+        let mut param_names = HashSet::new();
 
         if cursor.peek(0)?.ok_or(ParseError::AbruptEnd)?.kind()
             == &TokenKind::Punctuator(Punctuator::CloseParen)
@@ -76,6 +74,7 @@ where
         loop {
             let mut rest_param = false;
 
+            let position = cursor.peek(0)?.ok_or(ParseError::AbruptEnd)?.span().start();
             let next_param = match cursor.peek(0)? {
                 Some(tok) if tok.kind() == &TokenKind::Punctuator(Punctuator::Spread) => {
                     rest_param = true;
@@ -83,7 +82,11 @@ where
                 }
                 _ => FormalParameter::new(self.allow_yield, self.allow_await).parse(cursor)?,
             };
+            if param_names.contains(next_param.name()) {
+                return Err(ParseError::general("duplicate parameter name", position));
+            }
 
+            param_names.insert(Box::from(next_param.name()));
             params.push(next_param);
 
             if cursor.peek(0)?.ok_or(ParseError::AbruptEnd)?.kind()
diff --git a/boa/src/syntax/parser/function/tests.rs b/boa/src/syntax/parser/function/tests.rs
index a5d7c0b8bb..b6464dfce5 100644
--- a/boa/src/syntax/parser/function/tests.rs
+++ b/boa/src/syntax/parser/function/tests.rs
@@ -4,7 +4,7 @@ use crate::syntax::{
         Identifier, Node, Return,
     },
     ast::op::NumOp,
-    parser::tests::check_parser,
+    parser::{tests::check_parser, Parser},
 };
 
 /// Checks basic function declaration parsing.
@@ -21,6 +21,16 @@ fn check_basic() {
     );
 }
 
+/// Checks for duplicate parameter names.
+#[test]
+fn check_duplicates() {
+    let js = "function foo(a, a) {}";
+
+    let res = Parser::new(js.as_bytes(), false).parse_all();
+    dbg!(&res);
+    assert!(res.is_err());
+}
+
 /// Checks basic function declaration parsing with automatic semicolon insertion.
 #[test]
 fn check_basic_semicolon_insertion() {
diff --git a/boa/src/syntax/parser/mod.rs b/boa/src/syntax/parser/mod.rs
index f6b677a77c..3058cf5501 100644
--- a/boa/src/syntax/parser/mod.rs
+++ b/boa/src/syntax/parser/mod.rs
@@ -153,6 +153,6 @@ where
     type Output = StatementList;
 
     fn parse(self, cursor: &mut Cursor<R>) -> Result<Self::Output, ParseError> {
-        self::statement::StatementList::new(false, false, false, true, &[]).parse(cursor)
+        self::statement::StatementList::new(false, false, false, false, &[]).parse(cursor)
     }
 }