diff --git a/core/src/avm2/globals/object.rs b/core/src/avm2/globals/object.rs
index cdf1e04da..16597ecf5 100644
--- a/core/src/avm2/globals/object.rs
+++ b/core/src/avm2/globals/object.rs
@@ -12,7 +12,7 @@ use gc_arena::MutationContext;
 /// Implements `Object`
 pub fn constructor<'gc>(
     _avm: &mut Avm2<'gc>,
-    _action_context: &mut UpdateContext<'_, 'gc, '_>,
+    _context: &mut UpdateContext<'_, 'gc, '_>,
     _this: Option<Object<'gc>>,
     _args: &[Value<'gc>],
 ) -> Result<ReturnValue<'gc>, Error> {
@@ -22,7 +22,7 @@ pub fn constructor<'gc>(
 /// `Object.prototype.hasOwnProperty`
 pub fn has_own_property<'gc>(
     _avm: &mut Avm2<'gc>,
-    _action_context: &mut UpdateContext<'_, 'gc, '_>,
+    _context: &mut UpdateContext<'_, 'gc, '_>,
     this: Option<Object<'gc>>,
     args: &[Value<'gc>],
 ) -> Result<ReturnValue<'gc>, Error> {
@@ -39,6 +39,29 @@ pub fn has_own_property<'gc>(
     Ok(false.into())
 }
 
+/// `Object.prototype.isPrototypeOf`
+pub fn is_prototype_of<'gc>(
+    _avm: &mut Avm2<'gc>,
+    _context: &mut UpdateContext<'_, 'gc, '_>,
+    this: Option<Object<'gc>>,
+    args: &[Value<'gc>],
+) -> Result<ReturnValue<'gc>, Error> {
+    let search_proto: Result<Object<'gc>, Error> =
+        this.ok_or_else(|| "No valid this parameter".into());
+    let search_proto = search_proto?;
+    let mut target_proto = args.get(0).cloned().unwrap_or(Value::Undefined);
+
+    while let Value::Object(proto) = target_proto {
+        if Object::ptr_eq(search_proto, proto) {
+            return Ok(true.into());
+        }
+
+        target_proto = proto.proto().map(|o| o.into()).unwrap_or(Value::Undefined);
+    }
+
+    Ok(false.into())
+}
+
 /// Partially construct `Object.prototype`.
 ///
 /// `__proto__` and other cross-linked properties of this object will *not*
@@ -59,4 +82,10 @@ pub fn fill_proto<'gc>(
         0,
         FunctionObject::from_builtin(gc_context, has_own_property, fn_proto),
     );
+    object_proto.install_method(
+        gc_context,
+        QName::new(Namespace::public_namespace(), "isPrototypeOf"),
+        0,
+        FunctionObject::from_builtin(gc_context, is_prototype_of, fn_proto),
+    );
 }
diff --git a/core/tests/swfs/avm2/is_prototype_of/Test.as b/core/tests/swfs/avm2/is_prototype_of/Test.as
new file mode 100644
index 000000000..c23680bb7
--- /dev/null
+++ b/core/tests/swfs/avm2/is_prototype_of/Test.as
@@ -0,0 +1,28 @@
+package {
+	public class Test {}
+}
+
+class ES4Class extends Object {
+	
+}
+
+function ES3Class() {
+	
+}
+
+var es4inst = new ES4Class();
+var es3inst = new ES3Class();
+
+trace("//ES4Class.prototype.isPrototypeOf(es4inst);");
+trace(ES4Class.prototype.isPrototypeOf(es4inst));
+trace("//Object.prototype.isPrototypeOf(es4inst);");
+trace(Object.prototype.isPrototypeOf(es4inst));
+trace("//ES3Class.prototype.isPrototypeOf(es4inst);");
+trace(ES3Class.prototype.isPrototypeOf(es4inst));
+
+trace("//ES4Class.prototype.isPrototypeOf(es3inst);");
+trace(ES4Class.prototype.isPrototypeOf(es3inst));
+trace("//Object.prototype.isPrototypeOf(es3inst);");
+trace(Object.prototype.isPrototypeOf(es3inst));
+trace("//ES3Class.prototype.isPrototypeOf(es3inst);");
+trace(ES3Class.prototype.isPrototypeOf(es3inst));
\ No newline at end of file
diff --git a/core/tests/swfs/avm2/is_prototype_of/output.txt b/core/tests/swfs/avm2/is_prototype_of/output.txt
new file mode 100644
index 000000000..3d3f2dc80
--- /dev/null
+++ b/core/tests/swfs/avm2/is_prototype_of/output.txt
@@ -0,0 +1,13 @@
+
+//ES4Class.prototype.isPrototypeOf(es4inst);
+true
+//Object.prototype.isPrototypeOf(es4inst);
+true
+//ES3Class.prototype.isPrototypeOf(es4inst);
+false
+//ES4Class.prototype.isPrototypeOf(es3inst);
+false
+//Object.prototype.isPrototypeOf(es3inst);
+true
+//ES3Class.prototype.isPrototypeOf(es3inst);
+true
diff --git a/core/tests/swfs/avm2/is_prototype_of/test.fla b/core/tests/swfs/avm2/is_prototype_of/test.fla
new file mode 100644
index 000000000..e84226824
Binary files /dev/null and b/core/tests/swfs/avm2/is_prototype_of/test.fla differ
diff --git a/core/tests/swfs/avm2/is_prototype_of/test.swf b/core/tests/swfs/avm2/is_prototype_of/test.swf
new file mode 100644
index 000000000..ddbacb6f4
Binary files /dev/null and b/core/tests/swfs/avm2/is_prototype_of/test.swf differ