diff --git a/core/src/main/java/io/grpc/ClientCall.java b/core/src/main/java/io/grpc/ClientCall.java
index 6be5584..43ac85a 100644
--- a/core/src/main/java/io/grpc/ClientCall.java
+++ b/core/src/main/java/io/grpc/ClientCall.java
@@ -110,6 +110,9 @@
     /**
      * The response headers have been received. Headers always precede messages.
      *
+     * <p>Since {@link Metadata} is not thread-safe, the caller must not access (read or write)
+     * {@code headers} after this point.
+     *
      * @param headers containing metadata sent by the server at the start of the response.
      */
     public void onHeaders(Metadata headers) {}
@@ -127,6 +130,9 @@
      * processed by the server. No further receiving will occur and no further notifications will be
      * made.
      *
+     * <p>Since {@link Metadata} is not thread-safe, the caller must not access (read or write)
+     * {@code trailers} after this point.
+     *
      * <p>If {@code status} returns false for {@link Status#isOk()}, then the call failed.
      * An additional block of trailer metadata may be received at the end of the call from the
      * server. An empty {@link Metadata} object is passed if no trailers are received.
@@ -153,8 +159,10 @@
    * Start a call, using {@code responseListener} for processing response messages.
    *
    * <p>It must be called prior to any other method on this class, except for {@link #cancel} which
-   * may be called at any time. Since {@link Metadata} is not thread-safe, the caller must not
-   * access {@code headers} after this point.
+   * may be called at any time.
+   *
+   * <p>Since {@link Metadata} is not thread-safe, the caller must not access (read or write) {@code
+   * headers} after this point.
    *
    * @param responseListener receives response messages
    * @param headers which can contain extra call metadata, e.g. authentication credentials.
diff --git a/core/src/main/java/io/grpc/ServerCall.java b/core/src/main/java/io/grpc/ServerCall.java
index 42c2b62..f0b47bd 100644
--- a/core/src/main/java/io/grpc/ServerCall.java
+++ b/core/src/main/java/io/grpc/ServerCall.java
@@ -109,8 +109,8 @@
    * Send response header metadata prior to sending a response message. This method may
    * only be called once and cannot be called after calls to {@link #sendMessage} or {@link #close}.
    *
-   * <p>Since {@link Metadata} is not thread-safe, the caller must not access {@code headers} after
-   * this point.
+   * <p>Since {@link Metadata} is not thread-safe, the caller must not access (read or write) {@code
+   * headers} after this point.
    *
    * @param headers metadata to send prior to any response body.
    * @throws IllegalStateException if {@code close} has been called, a message has been sent, or
@@ -147,8 +147,8 @@
    * notification should be expected, independent of {@code status}. Otherwise {@link
    * Listener#onCancel} has been or will be called.
    *
-   * <p>Since {@link Metadata} is not thread-safe, the caller must not access {@code trailers} after
-   * this point.
+   * <p>Since {@link Metadata} is not thread-safe, the caller must not access (read or write) {@code
+   * trailers} after this point.
    *
    * @throws IllegalStateException if call is already {@code close}d
    */
diff --git a/core/src/main/java/io/grpc/ServerCallHandler.java b/core/src/main/java/io/grpc/ServerCallHandler.java
index ce57f15..f5ea9da 100644
--- a/core/src/main/java/io/grpc/ServerCallHandler.java
+++ b/core/src/main/java/io/grpc/ServerCallHandler.java
@@ -28,6 +28,9 @@
    * Produce a non-{@code null} listener for the incoming call. Implementations are free to call
    * methods on {@code call} before this method has returned.
    *
+   * <p>Since {@link Metadata} is not thread-safe, the caller must not access (read or write) {@code
+   * headers} after this point.
+   *
    * <p>If the implementation throws an exception, {@code call} will be closed with an error.
    * Implementations must not throw an exception if they started processing that may use {@code
    * call} on another thread.