diff --git a/.fernignore b/.fernignore
index 00097be7..3d51d3e2 100644
--- a/.fernignore
+++ b/.fernignore
@@ -7,4 +7,7 @@ LICENSE.md
 .github/workflows/semgrep.yml
 
 # Files that avoid breaking changes due to renames.
-src/merge/resources/accounting/types/currency_enum.py
\ No newline at end of file
+src/merge/resources/accounting/types/currency_enum.py
+
+# File that encodes enum query params as comma separated lists by default
+src/merge/core/query_encoder.py
diff --git a/src/merge/core/query_encoder.py b/src/merge/core/query_encoder.py
index 3183001d..559f93d5 100644
--- a/src/merge/core/query_encoder.py
+++ b/src/merge/core/query_encoder.py
@@ -24,6 +24,9 @@ def traverse_query_dict(dict_flat: Dict[str, Any], key_prefix: Optional[str] = N
 
 
 def single_query_encoder(query_key: str, query_value: Any) -> List[Tuple[str, Any]]:
+    # Special-case for 'expand' parameter: join lists into a comma-separated string
+    if query_key == "expand" and isinstance(query_value, list):
+        return [(query_key, ",".join(str(x) for x in query_value))]
     if isinstance(query_value, pydantic.BaseModel) or isinstance(query_value, dict):
         if isinstance(query_value, pydantic.BaseModel):
             obj_dict = query_value.dict(by_alias=True)