diff --git a/x509-tsp/src/generalized_time_nanos.rs b/x509-tsp/src/generalized_time_nanos.rs
index 965e84947..62230fbbb 100644
--- a/x509-tsp/src/generalized_time_nanos.rs
+++ b/x509-tsp/src/generalized_time_nanos.rs
@@ -2,7 +2,7 @@ use core::str::FromStr;
 use core::time::Duration;
 use der::{
     DateTime, DecodeValue, EncodeValue, ErrorKind, FixedTag, Header, Length, Reader, Result, Tag,
-    Writer,
+    Writer, asn1::GeneralizedTime,
 };
 
 /// ASN.1 `GeneralizedTime` type.
@@ -39,6 +39,15 @@ impl GeneralizedTimeNanos {
     }
 }
 
+impl From<GeneralizedTime> for GeneralizedTimeNanos {
+    fn from(time: GeneralizedTime) -> Self {
+        Self {
+            datetime: time.to_date_time(),
+            nanoseconds: 0,
+        }
+    }
+}
+
 /// Decode 2-digit decimal value
 #[allow(clippy::arithmetic_side_effects)]
 fn decode_decimal(tag: Tag, hi: u8, lo: u8) -> Result<u8> {