diff --git a/person_detection/base_camera.py b/person_detection/base_camera.py
index 96c148a..74b8f08 100644
--- a/person_detection/base_camera.py
+++ b/person_detection/base_camera.py
@@ -80,9 +80,9 @@
 
         return BaseCamera.frame
 
-    def frames():
+    def frames(self):
         """"Generator that returns frames from the camera."""
-        raise RuntimeError('Must be implemented by subclasses.')
+        raise NotImplementedError('Must be implemented by subclasses.')
 
     def _thread(self):
         """Camera background thread."""