diff --git a/moshi/src/main/java/com/squareup/moshi/JsonWriter.java b/moshi/src/main/java/com/squareup/moshi/JsonWriter.java
index fa4137b..bc2b9bd 100644
--- a/moshi/src/main/java/com/squareup/moshi/JsonWriter.java
+++ b/moshi/src/main/java/com/squareup/moshi/JsonWriter.java
@@ -445,7 +445,7 @@ public abstract class JsonWriter implements Closeable, Flushable {
    * <p>This method returns an opaque token. Callers must match all calls to this method with a call
    * to {@link #endFlatten} with the matching token.
    */
-  public final int beginFlatten() {
+  @CheckReturnValue public final int beginFlatten() {
     int context = peekScope();
     if (context != NONEMPTY_OBJECT && context != EMPTY_OBJECT
         && context != NONEMPTY_ARRAY && context != EMPTY_ARRAY) {