diff --git a/datagateway_api/common/icat/helpers.py b/datagateway_api/common/icat/helpers.py
index 73472cc9..e7859406 100644
--- a/datagateway_api/common/icat/helpers.py
+++ b/datagateway_api/common/icat/helpers.py
@@ -553,6 +553,7 @@ def get_facility_cycles_for_instrument(
 
     query_aggregate = "COUNT:DISTINCT" if count_query else "DISTINCT"
     query = ICATQuery(client, "FacilityCycle", aggregate=query_aggregate)
+    query.isis_endpoint = True
 
     instrument_id_check = PythonICATWhereFilter(
         "facility.instruments.id", instrument_id, "eq",
@@ -633,6 +634,7 @@ def get_investigations_for_instrument_in_facility_cycle(
 
     query_aggregate = "COUNT:DISTINCT" if count_query else "DISTINCT"
     query = ICATQuery(client, "Investigation", aggregate=query_aggregate)
+    query.isis_endpoint = True
 
     instrument_id_check = PythonICATWhereFilter(
         "facility.instruments.id", instrument_id, "eq",
diff --git a/datagateway_api/common/icat/query.py b/datagateway_api/common/icat/query.py
index 8da6c0fd..e57677f6 100644
--- a/datagateway_api/common/icat/query.py
+++ b/datagateway_api/common/icat/query.py
@@ -36,6 +36,9 @@ def __init__(
         :raises PythonICATError: If a ValueError is raised when creating a Query(), 500
             will be returned as a response
         """
+        # Needed for ISIS endpoints as they use DISTINCT keyword but don't select
+        # multiple attributes
+        self.isis_endpoint = False
 
         try:
             log.info("Creating ICATQuery for entity: %s", entity_name)
@@ -93,6 +96,7 @@ def execute_query(self, client, return_json_formattable=False):
             self.query.aggregate == "DISTINCT"
             and not count_query
             and not self.query.manual_count
+            and not self.isis_endpoint
         ):
             distinct_query = True
             log.info("Extracting the distinct fields from query's conditions")