diff --git a/build.gradle b/build.gradle
index 58be5c9398..badb1c8d39 100644
--- a/build.gradle
+++ b/build.gradle
@@ -143,6 +143,7 @@ subprojects {
             epoll_suffix = ":" + osdetector.classifier
         }
         libraries = [
+                errorprone: "com.google.errorprone:error_prone_annotations:2.0.11",
                 guava: "com.google.guava:guava:${guavaVersion}",
                 hpack: 'com.twitter:hpack:0.10.1',
                 jsr305: 'com.google.code.findbugs:jsr305:3.0.0',
diff --git a/core/build.gradle b/core/build.gradle
index f7ccc82a75..b03e06c9de 100644
--- a/core/build.gradle
+++ b/core/build.gradle
@@ -6,6 +6,7 @@ description = 'gRPC: Core'
 
 dependencies {
     compile libraries.guava,
+            libraries.errorprone,
             libraries.jsr305
     testCompile project(':grpc-testing')
 }
diff --git a/core/src/main/java/io/grpc/ClientCall.java b/core/src/main/java/io/grpc/ClientCall.java
index b3cac983e6..b253326e6c 100644
--- a/core/src/main/java/io/grpc/ClientCall.java
+++ b/core/src/main/java/io/grpc/ClientCall.java
@@ -31,6 +31,8 @@
 
 package io.grpc;
 
+import com.google.errorprone.annotations.DoNotMock;
+
 import javax.annotation.Nullable;
 
 /**
@@ -111,6 +113,7 @@ import javax.annotation.Nullable;
  * @param <ReqT> type of message sent one or more times to the server.
  * @param <RespT> type of message received one or more times from the server.
  */
+@DoNotMock("Use InProcessTransport and make a fake server instead")
 public abstract class ClientCall<ReqT, RespT> {
   /**
    * Callbacks for receiving metadata, response messages and completion status from the server.
diff --git a/core/src/main/java/io/grpc/ServerCall.java b/core/src/main/java/io/grpc/ServerCall.java
index 37977f365c..488438025f 100644
--- a/core/src/main/java/io/grpc/ServerCall.java
+++ b/core/src/main/java/io/grpc/ServerCall.java
@@ -31,6 +31,8 @@
 
 package io.grpc;
 
+import com.google.errorprone.annotations.DoNotMock;
+
 import java.net.SocketAddress;
 
 import javax.net.ssl.SSLSession;
@@ -52,6 +54,7 @@ import javax.net.ssl.SSLSession;
  * @param <ReqT> parsed type of request message.
  * @param <RespT> parsed type of response message.
  */
+@DoNotMock("Use InProcessTransport and make a fake server instead")
 public abstract class ServerCall<ReqT, RespT> {
   /**
    * {@link Attributes.Key} for the remote address of server call attributes