2 files changed, 2 insertions, 2 deletions
diff --git a/Libraries/LibJS/Runtime/GlobalObject.cpp b/Libraries/LibJS/Runtime/GlobalObject.cpp
index c1a344df30..b45fb867ca 100644
--- a/Libraries/LibJS/Runtime/GlobalObject.cpp
+++ b/Libraries/LibJS/Runtime/GlobalObject.cpp
@@ -21,7 +21,7 @@ GlobalObject::GlobalObject()
     put_native_function("isNaN", [](Object*, Vector<Value> arguments) -> Value {
         if (arguments.size() < 1)
             return js_undefined();
-        return Value(arguments[0].is_nan());
+        return Value(arguments[0].to_number().is_nan());
     });
     put("Math", heap().allocate<MathObject>());
 }
diff --git a/Libraries/LibJS/Tests/NaN-basic.js b/Libraries/LibJS/Tests/NaN-basic.js
index 94f271d35e..75ae62f16e 100644
--- a/Libraries/LibJS/Tests/NaN-basic.js
+++ b/Libraries/LibJS/Tests/NaN-basic.js
@@ -5,7 +5,7 @@ try {
     assert(nan + "" == "NaN");
     assert(isNaN(nan) === true);
     assert(isNaN(0) === false);
-    assert(isNaN(undefined) === false);
+    assert(isNaN(undefined) === true);
     assert(isNaN(null) === false);
     console.log("PASS");
 } catch (e) {