diff --git a/binding-mri/binding-mri.cpp b/binding-mri/binding-mri.cpp
index c28cdaa..f0a4bb4 100644
--- a/binding-mri/binding-mri.cpp
+++ b/binding-mri/binding-mri.cpp
@@ -80,6 +80,7 @@ RB_METHOD(mriP);
 RB_METHOD(mkxpDataDirectory);
 RB_METHOD(mkxpPuts);
 RB_METHOD(mkxpRawKeyStates);
+RB_METHOD(mkxpMouseInWindow);
 
 RB_METHOD(mriRgssMain);
 RB_METHOD(mriRgssStop);
@@ -144,6 +145,7 @@ static void mriBindingInit()
 	_rb_define_module_function(mod, "data_directory", mkxpDataDirectory);
 	_rb_define_module_function(mod, "puts", mkxpPuts);
 	_rb_define_module_function(mod, "raw_key_states", mkxpRawKeyStates);
+	_rb_define_module_function(mod, "mouse_in_window", mkxpMouseInWindow);
 
 	rb_gv_set("MKXP", Qtrue);
 }
@@ -222,6 +224,13 @@ RB_METHOD(mkxpRawKeyStates)
 	return str;
 }
 
+RB_METHOD(mkxpMouseInWindow)
+{
+	RB_UNUSED_PARAM;
+
+	return rb_bool_new(EventThread::mouseState.inWindow);
+}
+
 static VALUE rgssMainCb(VALUE block)
 {
 	rb_funcall2(block, rb_intern("call"), 0, 0);
diff --git a/src/input.cpp b/src/input.cpp
index d7978bd..22dab5d 100644
--- a/src/input.cpp
+++ b/src/input.cpp
@@ -665,9 +665,6 @@ int Input::mouseX()
 {
 	RGSSThreadData &rtData = shState->rtData();
 
-	if (!EventThread::mouseState.inWindow)
-		return -20;
-
 	return (EventThread::mouseState.x - rtData.screenOffset.x) * rtData.sizeResoRatio.x;
 }
 
@@ -675,9 +672,6 @@ int Input::mouseY()
 {
 	RGSSThreadData &rtData = shState->rtData();
 
-	if (!EventThread::mouseState.inWindow)
-		return -20;
-
 	return (EventThread::mouseState.y - rtData.screenOffset.y) * rtData.sizeResoRatio.y;
 }