diff --git a/drivers/input/sparse-keymap.c b/drivers/input/sparse-keymap.c
index 74bca5d..fdb6a39 100644
--- a/drivers/input/sparse-keymap.c
+++ b/drivers/input/sparse-keymap.c
@@ -209,6 +209,7 @@
 	}
 
 	if (test_bit(EV_KEY, dev->evbit)) {
+		__set_bit(KEY_UNKNOWN, dev->keybit);
 		__set_bit(EV_MSC, dev->evbit);
 		__set_bit(MSC_SCAN, dev->mscbit);
 	}
@@ -311,12 +312,19 @@
 {
 	const struct key_entry *ke =
 		sparse_keymap_entry_from_scancode(dev, code);
+	struct key_entry unknown_ke;
 
 	if (ke) {
 		sparse_keymap_report_entry(dev, ke, value, autorelease);
 		return true;
 	}
 
+	/* Report an unknown key event as a debugging aid */
+	unknown_ke.type = KE_KEY;
+	unknown_ke.code = code;
+	unknown_ke.keycode = KEY_UNKNOWN;
+	sparse_keymap_report_entry(dev, &unknown_ke, value, true);
+
 	return false;
 }
 EXPORT_SYMBOL(sparse_keymap_report_event);