diff --git a/src/APIHandler.py b/src/APIHandler.py
index 3bcef72..414772d 100644
--- a/src/APIHandler.py
+++ b/src/APIHandler.py
@@ -33,6 +33,8 @@ class APIHandler:
                     raise ConnectionError(f"Invalid API key or authentication method.")
                 case 404:
                     raise ConnectionError(f"404: Not Found. This means there's no resource with this elabid (wrong elabid?) on your eLabFTW (wrong endpoint?).")
+                case 400:
+                    raise ConnectionError(f"400: Bad Request. This means the API endpoint you tried to reach is invalid. Did you tamper with the source code? If not, contact the developer.")
                 case _:
                     raise ConnectionError(f"HTTP request failed with status code: {response.status_code} (NOTE: 4xx means user's fault).")
         else: