diff --git a/checks/normandy/uptake_error_rate.py b/checks/normandy/uptake_error_rate.py
index 6714d08b..ac7a2d07 100644
--- a/checks/normandy/uptake_error_rate.py
+++ b/checks/normandy/uptake_error_rate.py
@@ -51,7 +51,10 @@ async def run(
     by_collection: Dict[str, Dict[str, int]] = defaultdict(dict)
     for row in rows:
         rid = int(row["source"].split("/")[-1])
-        by_collection[rid][row["status"]] = row["total"]
+        # In Firefox 67, `custom_2_error` was used instead of `backoff`.
+        status = row["status"].replace("custom_2_error", "backoff")
+        by_collection[rid].setdefault(status, 0)
+        by_collection[rid][status] += row["total"]
 
     error_rates = {}
     for rid, all_statuses in by_collection.items():
diff --git a/tests/checks/normandy/test_normandy_uptake_error_rate.py b/tests/checks/normandy/test_normandy_uptake_error_rate.py
index 2cbb122e..caea0077 100644
--- a/tests/checks/normandy/test_normandy_uptake_error_rate.py
+++ b/tests/checks/normandy/test_normandy_uptake_error_rate.py
@@ -21,7 +21,14 @@
     {
         "status": "backoff",
         "source": "normandy/recipe/123",
-        "total": 5000,
+        "total": 4000,
+        "min_timestamp": "2019-09-16T01:36:12.348",
+        "max_timestamp": "2019-09-16T07:24:58.741",
+    },
+    {
+        "status": "custom_2_error",
+        "source": "normandy/recipe/123",
+        "total": 1000,
         "min_timestamp": "2019-09-16T01:36:12.348",
         "max_timestamp": "2019-09-16T07:24:58.741",
     },