diff --git a/test/functional/test_framework/script.py b/test/functional/test_framework/script.py
--- a/test/functional/test_framework/script.py
+++ b/test/functional/test_framework/script.py
@@ -478,16 +478,8 @@
         return other
 
     def __add__(self, other):
-        # Do the coercion outside of the try block so that errors in it are
-        # noticed.
-        other = self.__coerce_instance(other)
-
-        try:
-            # bytes.__add__ always returns bytes instances unfortunately
-            return CScript(super(CScript, self).__add__(other))
-        except TypeError:
-            raise TypeError(
-                'Can not add a {!r} instance to a CScript'.format(other.__class__))
+        # add makes no sense for a CScript()
+        raise NotImplementedError
 
     def join(self, iterable):
         # join makes no sense for a CScript()