diff --git a/src/domain/tls/certificate.rs b/src/domain/tls/certificate.rs
index 0eadf0e..0e8ee9a 100644
--- a/src/domain/tls/certificate.rs
+++ b/src/domain/tls/certificate.rs
@@ -35,6 +35,12 @@ impl Certificate {
             .set_subject_name(&name)
             .or_unexpected_while("setting subject name")?;
 
+        // 1970/01/01
+        let not_before = Asn1Time::from_unix(0).expect("initializing not_before");
+        builder
+            .set_not_before(not_before.as_ref())
+            .or_unexpected_while("setting not_before")?;
+
         // 9999/07/23
         let not_after = Asn1Time::from_unix(253388296800).expect("initializing not_after");
         builder