diff --git a/qds_sdk/commands.py b/qds_sdk/commands.py
index f241d63d..351737b0 100644
--- a/qds_sdk/commands.py
+++ b/qds_sdk/commands.py
@@ -1261,8 +1261,7 @@ def _read_iteratively(key_instance, fp, delim):
                 elif isinstance(fp, io.BufferedIOBase) or isinstance(fp, io.RawIOBase):
                     fp.write(data.decode('utf8').replace(chr(1), delim).encode('utf8'))
                 else:
-                    # Can this happen? Don't know what's the right thing to do in this case.
-                    pass
+                    raise ValueError('Only subclasses of io.TextIOBase or io.BufferedIOBase supported')
         except StopIteration:
             # Stream closes itself when the exception is raised
             return