diff --git a/Libraries/LibJS/Parser.cpp b/Libraries/LibJS/Parser.cpp
index 764ee67e85..893db52aad 100644
--- a/Libraries/LibJS/Parser.cpp
+++ b/Libraries/LibJS/Parser.cpp
@@ -1827,6 +1827,8 @@ Token Parser::consume_and_validate_numeric_literal()
     auto token = consume(TokenType::NumericLiteral);
     if (m_parser_state.m_strict_mode && is_unprefixed_octal_number(token.value()))
         syntax_error("Unprefixed octal number not allowed in strict mode", literal_start_line, literal_start_column);
+    if (match_identifier_name() && m_parser_state.m_current_token.trivia().is_empty())
+        syntax_error("Numeric literal must not be immediately followed by identifier");
     return token;
 }
 
diff --git a/Libraries/LibJS/Tests/numeric-literals-basic.js b/Libraries/LibJS/Tests/numeric-literals-basic.js
index 93a1815a49..f226581320 100644
--- a/Libraries/LibJS/Tests/numeric-literals-basic.js
+++ b/Libraries/LibJS/Tests/numeric-literals-basic.js
@@ -46,4 +46,6 @@ test("invalid numeric literals", () => {
     expect("0b").not.toEval();
     expect("0o").not.toEval();
     expect("'use strict'; 0755").not.toEval();
+    expect("1in[]").not.toEval();
+    expect("2instanceof foo").not.toEval();
 });