diff --git a/stub/src/main/java/io/grpc/stub/AbstractStub.java b/stub/src/main/java/io/grpc/stub/AbstractStub.java
index c33fa0821e..9a775c6512 100644
--- a/stub/src/main/java/io/grpc/stub/AbstractStub.java
+++ b/stub/src/main/java/io/grpc/stub/AbstractStub.java
@@ -18,6 +18,7 @@ package io.grpc.stub;
 
 import static com.google.common.base.Preconditions.checkNotNull;
 
+import com.google.errorprone.annotations.DoNotMock;
 import io.grpc.CallCredentials;
 import io.grpc.CallOptions;
 import io.grpc.Channel;
@@ -42,6 +43,7 @@ import javax.annotation.concurrent.ThreadSafe;
  * @param <S> the concrete type of this stub.
  */
 @ThreadSafe
+@DoNotMock
 public abstract class AbstractStub<S extends AbstractStub<S>> {
   private final Channel channel;
   private final CallOptions callOptions;
diff --git a/stub/src/main/java/io/grpc/stub/CallStreamObserver.java b/stub/src/main/java/io/grpc/stub/CallStreamObserver.java
index c194e94418..ab01cf255f 100644
--- a/stub/src/main/java/io/grpc/stub/CallStreamObserver.java
+++ b/stub/src/main/java/io/grpc/stub/CallStreamObserver.java
@@ -16,6 +16,7 @@
 
 package io.grpc.stub;
 
+import com.google.errorprone.annotations.DoNotMock;
 import io.grpc.ExperimentalApi;
 
 /**
@@ -36,6 +37,7 @@ import io.grpc.ExperimentalApi;
  *
  */
 @ExperimentalApi("https://github.com/grpc/grpc-java/issues/1788")
+@DoNotMock
 public abstract class CallStreamObserver<V> implements StreamObserver<V> {
 
   /**
diff --git a/stub/src/main/java/io/grpc/stub/ClientCallStreamObserver.java b/stub/src/main/java/io/grpc/stub/ClientCallStreamObserver.java
index ca49ad57a6..8a2509908d 100644
--- a/stub/src/main/java/io/grpc/stub/ClientCallStreamObserver.java
+++ b/stub/src/main/java/io/grpc/stub/ClientCallStreamObserver.java
@@ -16,6 +16,7 @@
 
 package io.grpc.stub;
 
+import com.google.errorprone.annotations.DoNotMock;
 import io.grpc.ExperimentalApi;
 
 import javax.annotation.Nullable;
@@ -25,6 +26,7 @@ import javax.annotation.Nullable;
  * client calls.
  */
 @ExperimentalApi("https://github.com/grpc/grpc-java/issues/1788")
+@DoNotMock
 public abstract class ClientCallStreamObserver<V> extends CallStreamObserver<V> {
   /**
    * Prevent any further processing for this {@code ClientCallStreamObserver}. No further messages
diff --git a/stub/src/main/java/io/grpc/stub/ServerCallStreamObserver.java b/stub/src/main/java/io/grpc/stub/ServerCallStreamObserver.java
index bfe25e33dc..0f5c3d3752 100644
--- a/stub/src/main/java/io/grpc/stub/ServerCallStreamObserver.java
+++ b/stub/src/main/java/io/grpc/stub/ServerCallStreamObserver.java
@@ -16,6 +16,7 @@
 
 package io.grpc.stub;
 
+import com.google.errorprone.annotations.DoNotMock;
 import io.grpc.ExperimentalApi;
 
 /**
@@ -23,6 +24,7 @@ import io.grpc.ExperimentalApi;
  * cancellation events on the server side.
  */
 @ExperimentalApi("https://github.com/grpc/grpc-java/issues/1788")
+@DoNotMock
 public abstract class ServerCallStreamObserver<V> extends CallStreamObserver<V> {
 
   /**