diff --git a/Userland/Libraries/LibJS/Runtime/WeakMapConstructor.cpp b/Userland/Libraries/LibJS/Runtime/WeakMapConstructor.cpp
index 5ef3121fb7..a3fe694d8c 100644
--- a/Userland/Libraries/LibJS/Runtime/WeakMapConstructor.cpp
+++ b/Userland/Libraries/LibJS/Runtime/WeakMapConstructor.cpp
@@ -36,6 +36,7 @@ Value WeakMapConstructor::call()
     return {};
 }
 
+// 24.3.1.1 WeakMap ( [ iterable ] ), https://tc39.es/ecma262/#sec-weakmap-iterable
 Value WeakMapConstructor::construct(Function&)
 {
     auto& vm = this->vm();
@@ -57,10 +58,10 @@ Value WeakMapConstructor::construct(Function&)
             vm.throw_exception<TypeError>(global_object(), ErrorType::NotAnObject, String::formatted("Iterator value {}", iterator_value.to_string_without_side_effects()));
             return IterationDecision::Break;
         }
-        auto key = iterator_value.as_object().get(0);
+        auto key = iterator_value.as_object().get(0).value_or(js_undefined());
         if (vm.exception())
             return IterationDecision::Break;
-        auto value = iterator_value.as_object().get(1);
+        auto value = iterator_value.as_object().get(1).value_or(js_undefined());
         if (vm.exception())
             return IterationDecision::Break;
         (void)vm.call(adder.as_function(), Value(weak_map), key, value);
diff --git a/Userland/Libraries/LibJS/Tests/builtins/WeakMap/WeakMap.js b/Userland/Libraries/LibJS/Tests/builtins/WeakMap/WeakMap.js
index 9dcbe59fb9..78c8ad79a9 100644
--- a/Userland/Libraries/LibJS/Tests/builtins/WeakMap/WeakMap.js
+++ b/Userland/Libraries/LibJS/Tests/builtins/WeakMap/WeakMap.js
@@ -32,3 +32,11 @@ describe("normal behavior", () => {
         expect(a instanceof WeakMap).toBeTrue();
     });
 });
+
+describe("regressions", () => {
+    test("missing key/value properties on iterable entry", () => {
+        expect(() => {
+            new WeakMap([{}]);
+        }).toThrowWithMessage(TypeError, "undefined is not an object");
+    });
+});