diff --git a/sros2/sros2/keystore/_permission.py b/sros2/sros2/keystore/_permission.py
index eb2f20db..2026b4f2 100644
--- a/sros2/sros2/keystore/_permission.py
+++ b/sros2/sros2/keystore/_permission.py
@@ -12,6 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import datetime
 import os
 import pathlib