diff --git a/superset/db_engine_specs/bigquery.py b/superset/db_engine_specs/bigquery.py
index e33457c79ab..51fd710ab33 100644
--- a/superset/db_engine_specs/bigquery.py
+++ b/superset/db_engine_specs/bigquery.py
@@ -123,8 +123,12 @@ class BigQueryEngineSpec(BaseEngineSpec):
 
     _time_grain_expressions = {
         None: "{col}",
-        "PT1S": "{func}({col}, SECOND)",
-        "PT1M": "{func}({col}, MINUTE)",
+        "PT1S": "CAST(TIMESTAMP_SECONDS("
+        "UNIX_SECONDS(CAST({col} AS TIMESTAMP))"
+        ") AS {type})",
+        "PT1M": "CAST(TIMESTAMP_SECONDS("
+        "60 * DIV(UNIX_SECONDS(CAST({col} AS TIMESTAMP)), 60)"
+        ") AS {type})",
         "PT5M": "CAST(TIMESTAMP_SECONDS("
         "5*60 * DIV(UNIX_SECONDS(CAST({col} AS TIMESTAMP)), 5*60)"
         ") AS {type})",