diff --git a/serde/src/ser/impls.rs b/serde/src/ser/impls.rs
index 803c739e..0a6c3d46 100644
--- a/serde/src/ser/impls.rs
+++ b/serde/src/ser/impls.rs
@@ -616,7 +616,7 @@ impl Serialize for SystemTime {
         use super::SerializeStruct;
         let duration_since_epoch = self
             .duration_since(UNIX_EPOCH)
-            .expect("SystemTime must be later than UNIX_EPOCH");
+            .map_err(|_|S::Error::custom("SystemTime must be later than UNIX_EPOCH"))?;
         let mut state = try!(serializer.serialize_struct("SystemTime", 2));
         try!(state.serialize_field("secs_since_epoch", &duration_since_epoch.as_secs()));
         try!(state.serialize_field("nanos_since_epoch", &duration_since_epoch.subsec_nanos()));