diff --git a/google-http-client/src/main/java/com/google/api/client/util/DateTime.java b/google-http-client/src/main/java/com/google/api/client/util/DateTime.java
index 4caf768ce..2aa914e9c 100644
--- a/google-http-client/src/main/java/com/google/api/client/util/DateTime.java
+++ b/google-http-client/src/main/java/com/google/api/client/util/DateTime.java
@@ -292,6 +292,8 @@ public static SecondsAndNanos parseRfc3339ToSecondsAndNanos(String str) {
 
   /** A timestamp represented as the number of seconds and nanoseconds since Epoch. */
   public static final class SecondsAndNanos implements Serializable {
+    private static long serialVersionUID = 1L;
+
     private final long seconds;
     private final int nanos;
 
@@ -337,6 +339,8 @@ public String toString() {
 
   /** Result of parsing an RFC 3339 string. */
   private static class Rfc3339ParseResult implements Serializable {
+    private static final long serialVersionUID = 1L;
+
     private final long seconds;
     private final int nanos;
     private final boolean timeGiven;