diff --git a/sdk/src/main/java/com/bugsnag/android/NativeInterface.java b/sdk/src/main/java/com/bugsnag/android/NativeInterface.java
index caee5ee7d4..be4fe7c057 100644
--- a/sdk/src/main/java/com/bugsnag/android/NativeInterface.java
+++ b/sdk/src/main/java/com/bugsnag/android/NativeInterface.java
@@ -399,11 +399,12 @@ public static void setNotifyReleaseStages(@Nullable String[] notifyReleaseStages
     /**
      * Update the current session with a given start time, ID, and event counts
      */
-    public static void registerSession(long startedAt, @NonNull String sessionId,
+    public static void registerSession(long startedAt, @Nullable String sessionId,
                                        int unhandledCount, int handledCount) {
         Client client = getClient();
         User user = client.getUser();
-        client.getSessionTracker().registerExistingSession(new Date(startedAt), sessionId, user,
+        Date startDate = startedAt > 0 ? new Date(startedAt) : null;
+        client.getSessionTracker().registerExistingSession(startDate, sessionId, user,
                                                            unhandledCount, handledCount);
     }
 
diff --git a/sdk/src/main/java/com/bugsnag/android/SessionTracker.java b/sdk/src/main/java/com/bugsnag/android/SessionTracker.java
index e6434842e9..ea5c422ae8 100644
--- a/sdk/src/main/java/com/bugsnag/android/SessionTracker.java
+++ b/sdk/src/main/java/com/bugsnag/android/SessionTracker.java
@@ -89,10 +89,13 @@ class SessionTracker extends Observable implements Application.ActivityLifecycle
      * @param handledCount   the number of handled events which have occurred during the session
      * @return the session
      */
-    @Nullable Session registerExistingSession(@NonNull Date date, @NonNull String sessionId,
+    @Nullable Session registerExistingSession(@Nullable Date date, @Nullable String sessionId,
                                               @Nullable User user, int unhandledCount,
                                               int handledCount) {
-        Session session = new Session(sessionId, date, user, unhandledCount, handledCount);
+        Session session = null;
+        if (date != null && sessionId != null) {
+            session = new Session(sessionId, date, user, unhandledCount, handledCount);
+        }
         currentSession.set(session);
         return session;
     }