diff --git a/api/tools/prepare_sql_tiles.py b/api/tools/prepare_sql_tiles.py
index 2833fb5..599a7f5 100755
--- a/api/tools/prepare_sql_tiles.py
+++ b/api/tools/prepare_sql_tiles.py
@@ -32,6 +32,32 @@ EXTRA_ARGS = [
 ]
 
 
+class CustomMvtGenerator(MvtGenerator):
+    def generate_sqltomvt_func(self, fname, extra_args: List[Tuple[str, str]]) -> str:
+        """
+        Creates a SQL function that returns a single bytea value or null. This
+        method is overridden to allow for custom arguments in the created function
+        """
+        extra_args_types = "".join([f", {a[1]}" for a in extra_args])
+        extra_args_definitions = "".join(
+            [f", {a[0]} {a[1]} DEFAULT {a[2]}" for a in extra_args]
+        )
+
+        return f"""\
+DROP FUNCTION IF EXISTS {fname}(integer, integer, integer{extra_args_types});
+CREATE FUNCTION {fname}(zoom integer, x integer, y integer{extra_args_definitions})
+RETURNS {'TABLE(mvt bytea, key text)' if self.key_column else 'bytea'} AS $$
+{self.generate_sql()};
+$$ LANGUAGE SQL STABLE RETURNS NULL ON NULL INPUT;"""
+
+EXTRA_ARGS = [
+    # name, type, default
+    ("user_id", "integer", "NULL"),
+    ("min_time", "timestamp", "NULL"),
+    ("max_time", "timestamp", "NULL"),
+]
+
+
 class CustomMvtGenerator(MvtGenerator):
     def generate_sqltomvt_func(self, fname, extra_args: List[Tuple[str, str]]) -> str:
         """
diff --git a/tile-generator/layers/obs_events/layer.sql b/tile-generator/layers/obs_events/layer.sql
index 6c4c5cd..ec6c9af 100644
--- a/tile-generator/layers/obs_events/layer.sql
+++ b/tile-generator/layers/obs_events/layer.sql
@@ -12,11 +12,11 @@ RETURNS TABLE(event_id bigint, geometry geometry, distance_overtaker float, dist
       CASE WHEN road.zone IS NULL THEN 'urban' else road.zone END as zone,
       overtaking_event.way_id::bigint as way_id
     FROM overtaking_event
-    FULL OUTER JOIN road ON road.way_id = overtaking_event.way_id
+    FULL OUTER JOIN road ON (road.way_id = overtaking_event.way_id)
     JOIN track on track.id = overtaking_event.track_id
     WHERE
       zoom_level >= 10 AND
-      ST_Transform(overtaking_event.geometry, 3857) && bbox
+      ST_Transform(overtaking_event.geometry, 3857) && bbox;
       AND (user_id is NULL OR user_id = track.author_id)
       AND time BETWEEN COALESCE(min_time, '1900-01-01'::timestamp) AND COALESCE(max_time, '2100-01-01'::timestamp);