diff --git a/Libraries/LibJS/Runtime/FunctionPrototype.cpp b/Libraries/LibJS/Runtime/FunctionPrototype.cpp
index 68a90b57d3..f0aa7041b1 100644
--- a/Libraries/LibJS/Runtime/FunctionPrototype.cpp
+++ b/Libraries/LibJS/Runtime/FunctionPrototype.cpp
@@ -71,10 +71,8 @@ Value FunctionPrototype::apply(Interpreter& interpreter)
         return interpreter.call(function, this_arg);
     if (!arg_array.is_object())
         return interpreter.throw_exception<TypeError>("argument array must be an object");
-    size_t length = 0;
     auto length_property = arg_array.as_object().get("length");
-    if (!length_property.is_empty())
-        length = length_property.to_number().to_i32();
+    auto length = length_property.to_size_t();
     MarkedValueList arguments(interpreter.heap());
     for (size_t i = 0; i < length; ++i) {
         auto element = arg_array.as_object().get(String::number(i));
diff --git a/Libraries/LibJS/Runtime/Value.cpp b/Libraries/LibJS/Runtime/Value.cpp
index 7faabd419e..8e6385ee73 100644
--- a/Libraries/LibJS/Runtime/Value.cpp
+++ b/Libraries/LibJS/Runtime/Value.cpp
@@ -183,6 +183,16 @@ double Value::to_double() const
     return to_number().as_double();
 }
 
+size_t Value::to_size_t() const
+{
+    if (is_empty())
+        return 0;
+    auto number = to_number();
+    if (number.is_nan() || number.as_double() <= 0)
+        return 0;
+    return min(number.to_i32(), (i32)pow(2, 53) - 1);
+}
+
 Value greater_than(Interpreter&, Value lhs, Value rhs)
 {
     return Value(lhs.to_number().as_double() > rhs.to_number().as_double());
@@ -313,7 +323,7 @@ Value mod(Interpreter&, Value lhs, Value rhs)
 
     double index = lhs.to_number().as_double();
     double period = rhs.to_number().as_double();
-    double trunc = (double)(i32) (index / period);
+    double trunc = (double)(i32)(index / period);
 
     return Value(index - trunc * period);
 }
diff --git a/Libraries/LibJS/Runtime/Value.h b/Libraries/LibJS/Runtime/Value.h
index 86a513806e..48d8cc4c10 100644
--- a/Libraries/LibJS/Runtime/Value.h
+++ b/Libraries/LibJS/Runtime/Value.h
@@ -162,6 +162,7 @@ public:
     Value to_number() const;
     i32 to_i32() const;
     double to_double() const;
+    size_t to_size_t() const;
     Value to_primitive(Interpreter&) const;
 
     Object* to_object(Heap&) const;