diff --git a/Userland/Libraries/LibJS/Bytecode/Generator.cpp b/Userland/Libraries/LibJS/Bytecode/Generator.cpp
index 290829b2b6..f7b6b5b4f2 100644
--- a/Userland/Libraries/LibJS/Bytecode/Generator.cpp
+++ b/Userland/Libraries/LibJS/Bytecode/Generator.cpp
@@ -120,7 +120,7 @@ CodeGenerationErrorOr<void> Generator::emit_function_declaration_instantiation(E
             }
         }
     } else {
-        emit<Op::CreateVariableEnvironment>();
+        emit<Op::CreateVariableEnvironment>(function.m_var_environment_bindings_count);
 
         if (scope_body) {
             for (auto const& variable_to_initialize : function.m_var_names_to_initialize_binding) {
@@ -158,7 +158,7 @@ CodeGenerationErrorOr<void> Generator::emit_function_declaration_instantiation(E
     if (!function.m_strict) {
         bool can_elide_declarative_environment = !function.m_contains_direct_call_to_eval && (!scope_body || !scope_body->has_non_local_lexical_declarations());
         if (!can_elide_declarative_environment) {
-            emit<Op::CreateLexicalEnvironment>();
+            emit<Op::CreateLexicalEnvironment>(function.m_lex_environment_bindings_count);
         }
     }
 
diff --git a/Userland/Libraries/LibJS/Bytecode/Interpreter.cpp b/Userland/Libraries/LibJS/Bytecode/Interpreter.cpp
index 22f2895c26..d39b0cbd15 100644
--- a/Userland/Libraries/LibJS/Bytecode/Interpreter.cpp
+++ b/Userland/Libraries/LibJS/Bytecode/Interpreter.cpp
@@ -1256,7 +1256,9 @@ ThrowCompletionOr<void> DeleteVariable::execute_impl(Bytecode::Interpreter& inte
 void CreateLexicalEnvironment::execute_impl(Bytecode::Interpreter& interpreter) const
 {
     auto make_and_swap_envs = [&](auto& old_environment) {
-        GCPtr<Environment> environment = new_declarative_environment(*old_environment).ptr();
+        auto declarative_environment = new_declarative_environment(*old_environment).ptr();
+        declarative_environment->ensure_capacity(m_capacity);
+        GCPtr<Environment> environment = declarative_environment;
         swap(old_environment, environment);
         return environment;
     };
@@ -1268,6 +1270,7 @@ ThrowCompletionOr<void> CreateVariableEnvironment::execute_impl(Bytecode::Interp
 {
     auto& running_execution_context = interpreter.vm().running_execution_context();
     auto var_environment = new_declarative_environment(*running_execution_context.lexical_environment);
+    var_environment->ensure_capacity(m_capacity);
     running_execution_context.variable_environment = var_environment;
     running_execution_context.lexical_environment = var_environment;
     return {};
diff --git a/Userland/Libraries/LibJS/Bytecode/Op.h b/Userland/Libraries/LibJS/Bytecode/Op.h
index 661a7b25d9..970d2c2bd9 100644
--- a/Userland/Libraries/LibJS/Bytecode/Op.h
+++ b/Userland/Libraries/LibJS/Bytecode/Op.h
@@ -443,24 +443,32 @@ enum class EnvironmentMode {
 
 class CreateLexicalEnvironment final : public Instruction {
 public:
-    explicit CreateLexicalEnvironment()
+    explicit CreateLexicalEnvironment(u32 capacity = 0)
         : Instruction(Type::CreateLexicalEnvironment)
+        , m_capacity(capacity)
     {
     }
 
     void execute_impl(Bytecode::Interpreter&) const;
     ByteString to_byte_string_impl(Bytecode::Executable const&) const;
+
+private:
+    u32 m_capacity { 0 };
 };
 
 class CreateVariableEnvironment final : public Instruction {
 public:
-    explicit CreateVariableEnvironment()
+    explicit CreateVariableEnvironment(u32 capacity = 0)
         : Instruction(Type::CreateVariableEnvironment)
+        , m_capacity(capacity)
     {
     }
 
     ThrowCompletionOr<void> execute_impl(Bytecode::Interpreter&) const;
     ByteString to_byte_string_impl(Bytecode::Executable const&) const;
+
+private:
+    u32 m_capacity { 0 };
 };
 
 class EnterObjectEnvironment final : public Instruction {