diff --git a/CHANGELOG.md b/CHANGELOG.md
index 865390d8e..007c5ddff 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,8 @@
 
 * Fix certificate generation for punycode domains.
   ([#6382](https://github.com/mitmproxy/mitmproxy/pull/6382), @mhils)
+* Fix a bug that would crash mitmweb when opening options.
+  ([#6386](https://github.com/mitmproxy/mitmproxy/pull/6386), @mhils)
 
 
 ## 24 September 2023: mitmproxy 10.1.0
diff --git a/mitmproxy/addonmanager.py b/mitmproxy/addonmanager.py
index e0c5ef86a..d587b6bb3 100644
--- a/mitmproxy/addonmanager.py
+++ b/mitmproxy/addonmanager.py
@@ -82,6 +82,7 @@ class Loader:
         reflowed by tools. Information on the data type should be omitted -
         it will be generated and added by tools as needed.
         """
+        assert not isinstance(choices, str)
         if name in self.master.options:
             existing = self.master.options._options[name]
             same_signature = (
diff --git a/mitmproxy/addons/savehar.py b/mitmproxy/addons/savehar.py
index 8f80cd354..09ff6ce97 100644
--- a/mitmproxy/addons/savehar.py
+++ b/mitmproxy/addons/savehar.py
@@ -78,9 +78,11 @@ class SaveHar:
             "hardump",
             str,
             "",
-            "Save a HAR file with all flows on exit. "
-            "You may select particular flows by setting save_stream_filter.",
-            "For mitmdump, enabling this option will mean that flows are kept in memory. ",
+            """
+            Save a HAR file with all flows on exit.
+            You may select particular flows by setting save_stream_filter.
+            For mitmdump, enabling this option will mean that flows are kept in memory.
+            """,
         )
 
     def configure(self, updated):