diff --git a/internal/api/scim/integration_test/users_list_test.go b/internal/api/scim/integration_test/users_list_test.go
index 19268880f..36dc96210 100644
--- a/internal/api/scim/integration_test/users_list_test.go
+++ b/internal/api/scim/integration_test/users_list_test.go
@@ -93,6 +93,14 @@ func TestListUser(t *testing.T) {
 			wantErr:   true,
 			errorType: "invalidValue",
 		},
+		{
+			name: "custom sort field",
+			req: &scim.ListRequest{
+				SortBy: gu.Ptr("externalid"),
+			},
+			wantErr:   true,
+			errorType: "invalidValue",
+		},
 		{
 			name: "unknown filter field",
 			req: &scim.ListRequest{
diff --git a/internal/api/scim/resources/resource_list.go b/internal/api/scim/resources/resource_list.go
index aa790e44d..ebd648d7a 100644
--- a/internal/api/scim/resources/resource_list.go
+++ b/internal/api/scim/resources/resource_list.go
@@ -118,7 +118,7 @@ func (r *ListRequest) toSearchRequest(defaultSortCol query.Column, fieldPathColu
 	if r.SortBy == "" {
 		// set a default sort to ensure consistent results
 		sr.SortingColumn = defaultSortCol
-	} else if sortCol, err := fieldPathColumnMapping.Resolve(r.SortBy); err != nil {
+	} else if sortCol, err := fieldPathColumnMapping.Resolve(r.SortBy); err != nil || sortCol.FieldType == filter.FieldTypeCustom {
 		return sr, serrors.ThrowInvalidValue(zerrors.ThrowInvalidArgument(err, "SCIM-SRT1", "SortBy field is unknown or not supported"))
 	} else {
 		sr.SortingColumn = sortCol.Column