diff --git a/cql3/statements/sl_prop_defs.cc b/cql3/statements/sl_prop_defs.cc
index 6e86418582..70a5d3fd5e 100644
--- a/cql3/statements/sl_prop_defs.cc
+++ b/cql3/statements/sl_prop_defs.cc
@@ -38,6 +38,12 @@ void sl_prop_defs::validate() {
         }
         data_value v = duration_type->deserialize(duration_type->from_string(*repr));
         cql_duration duration = static_pointer_cast<const duration_type_impl>(duration_type)->from_value(v);
+        if (duration.months || duration.days) {
+            throw exceptions::invalid_request_exception("Timeout values cannot be longer than 24h");
+        }
+        if (duration.nanoseconds % 1'000'000 != 0) {
+            throw exceptions::invalid_request_exception("Timeout values must be expressed in millisecond granularity");
+        }
         return std::chrono::duration_cast<lowres_clock::duration>(std::chrono::nanoseconds(duration.nanoseconds));
     };
 
diff --git a/db/system_distributed_keyspace.cc b/db/system_distributed_keyspace.cc
index 250376be39..b3df493ded 100644
--- a/db/system_distributed_keyspace.cc
+++ b/db/system_distributed_keyspace.cc
@@ -598,10 +598,20 @@ future<qos::service_levels_info> system_distributed_keyspace::get_service_level(
 future<> system_distributed_keyspace::set_service_level(sstring service_level_name, qos::service_level_options slo) const {
     static sstring prepared_query = format("INSERT INTO {}.{} (service_level) VALUES (?);", NAME, SERVICE_LEVELS);
     co_await _qp.execute_internal(prepared_query, db::consistency_level::ONE, internal_distributed_query_state(), {service_level_name});
-    auto to_data_value = [&] (const std::optional<lowres_clock::duration>& d) {
-        return d
-                ? data_value(cql_duration(months_counter{0}, days_counter{0}, nanoseconds_counter{std::chrono::duration_cast<std::chrono::nanoseconds>(*d).count()}))
-                : data_value::make_null(duration_type);
+    auto to_data_value = [&] (const qos::service_level_options::timeout_type& tv) {
+        return std::visit(overloaded_functor {
+            [&] (const qos::service_level_options::unset_marker&) {
+                return data_value::make_null(duration_type);
+            },
+            [&] (const qos::service_level_options::delete_marker&) {
+                return data_value::make_null(duration_type);
+            },
+            [&] (const lowres_clock::duration& d) {
+                return data_value(cql_duration(months_counter{0},
+                        days_counter{0},
+                        nanoseconds_counter{std::chrono::duration_cast<std::chrono::nanoseconds>(d).count()}));
+            },
+        }, tv);
     };
     co_await _qp.execute_internal(format("UPDATE {}.{} SET timeout = ? WHERE service_level = ?;", NAME, SERVICE_LEVELS),
                 db::consistency_level::ONE,