diff --git a/src/main/java/com/google/api/gax/grpc/ApiCallable.java b/src/main/java/com/google/api/gax/grpc/ApiCallable.java
index b1069073d..ccbf65ab4 100644
--- a/src/main/java/com/google/api/gax/grpc/ApiCallable.java
+++ b/src/main/java/com/google/api/gax/grpc/ApiCallable.java
@@ -109,7 +109,7 @@ public final class ApiCallable<RequestT, ResponseT> {
    * @param simpleCallSettings {@link com.google.api.gax.grpc.SimpleCallSettings} to configure the
    * method-level settings with.
    * @param channel {@link ManagedChannel} to use to connect to the service.
-   * @param executor {@link ScheduledExecutorService} to use to when connecting to the service.
+   * @param executor {@link ScheduledExecutorService} to use when connecting to the service.
    * @return {@link com.google.api.gax.grpc.ApiCallable} callable object.
    */
   public static <RequestT, ResponseT> ApiCallable<RequestT, ResponseT> create(
diff --git a/src/main/java/com/google/api/gax/grpc/ChannelProvider.java b/src/main/java/com/google/api/gax/grpc/ChannelProvider.java
index 23daa349e..3b0020e47 100644
--- a/src/main/java/com/google/api/gax/grpc/ChannelProvider.java
+++ b/src/main/java/com/google/api/gax/grpc/ChannelProvider.java
@@ -8,7 +8,6 @@
 import java.util.concurrent.Executor;
 
 import javax.annotation.Nullable;
-import javax.naming.OperationNotSupportedException;
 
 /**
  * Provides an interface to hold and build the channel that will be used. If the channel does not
@@ -19,9 +18,9 @@
  * where the same {@link ManagedChannel} instance is returned, for example by a
  * {@link ChannelProvider} created using the {@link ServiceApiSettings}
  * provideChannelWith(ManagedChannel, boolean) method, and shouldAutoClose returns true, the
- * {@link #getChannel} method will throw an {@link OperationNotSupportedException} if it is called
- * more than once. This is to prevent the same {@link ManagedChannel} being closed prematurely when
- * it is used by multiple client objects.
+ * {@link #getChannel} method will throw an {@link IllegalStateException} if it is called more than
+ * once. This is to prevent the same {@link ManagedChannel} being closed prematurely when it is used
+ * by multiple client objects.
  */
 public interface ChannelProvider {
   /**
@@ -42,8 +41,8 @@ public interface ChannelProvider {
    *
    * If the {@link ChannelProvider} is configured to return a fixed {@link ManagedChannel} object
    * and to return shouldAutoClose as true, then after the first call to {@link #getChannel},
-   * subsequent calls should throw an {@link OperationNotSupportedException}. See interface level
-   * docs for {@link ChannelProvider} for more details.
+   * subsequent calls should throw an {@link IllegalStateException}. See interface level docs for
+   * {@link ChannelProvider} for more details.
    */
-  ManagedChannel getChannel(Executor executor) throws IOException, OperationNotSupportedException;
+  ManagedChannel getChannel(Executor executor) throws IOException, IllegalStateException;
 }
diff --git a/src/main/java/com/google/api/gax/grpc/ExecutorProvider.java b/src/main/java/com/google/api/gax/grpc/ExecutorProvider.java
index 5a26a5133..03d4ce054 100644
--- a/src/main/java/com/google/api/gax/grpc/ExecutorProvider.java
+++ b/src/main/java/com/google/api/gax/grpc/ExecutorProvider.java
@@ -2,8 +2,6 @@
 
 import java.util.concurrent.ScheduledExecutorService;
 
-import javax.naming.OperationNotSupportedException;
-
 /**
  * Provides an interface to hold and create the Executor to be used. If the executor does not
  * already exist, it will be constructed when {@link #getExecutor} is called.
@@ -13,9 +11,9 @@
  * instance. In cases where the same {@link ScheduledExecutorService} instance is returned, for
  * example by an {@link ExecutorProvider} created using the {@link ServiceApiSettings}
  * provideExecutorWith(ScheduledExecutorService, boolean) method, and shouldAutoClose returns true,
- * the {@link #getExecutor} method will throw an {@link OperationNotSupportedException} if it is
- * called more than once. This is to prevent the same {@link ScheduledExecutorService} being closed
- * prematurely when it is used by multiple client objects.
+ * the {@link #getExecutor} method will throw an {@link IllegalStateException} if it is called more
+ * than once. This is to prevent the same {@link ScheduledExecutorService} being closed prematurely
+ * when it is used by multiple client objects.
  */
 public interface ExecutorProvider {
   /**
@@ -29,8 +27,9 @@ public interface ExecutorProvider {
    *
    * If the {@link ExecutorProvider} is configured to return a fixed
    * {@link ScheduledExecutorService} object and to return shouldAutoClose as true, then after the
-   * first call to {@link #getExecutor}, subsequent calls should throw an {@link ExecutorProvider}.
-   * See interface level docs for {@link ExecutorProvider} for more details.
+   * first call to {@link #getExecutor}, subsequent calls should throw an
+   * {@link IllegalStateException}. See interface level docs for {@link ExecutorProvider} for more
+   * details.
    */
-  ScheduledExecutorService getExecutor() throws OperationNotSupportedException;
+  ScheduledExecutorService getExecutor() throws IllegalStateException;
 }
diff --git a/src/main/java/com/google/api/gax/grpc/ServiceApiSettings.java b/src/main/java/com/google/api/gax/grpc/ServiceApiSettings.java
index 5c200ea24..a13a19ce1 100644
--- a/src/main/java/com/google/api/gax/grpc/ServiceApiSettings.java
+++ b/src/main/java/com/google/api/gax/grpc/ServiceApiSettings.java
@@ -19,8 +19,6 @@
 import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.ScheduledThreadPoolExecutor;
 
-import javax.naming.OperationNotSupportedException;
-
 /**
  * A base settings class to configure a service API class.
  *
@@ -81,8 +79,7 @@ protected ServiceApiSettings(
    * Return the channel to be used to connect to the service, retrieved using the channelProvider.
    * If no channel was set, a default channel will be instantiated.
    */
-  public final ManagedChannel getOrBuildChannel()
-      throws IOException, OperationNotSupportedException {
+  public final ManagedChannel getOrBuildChannel() throws IOException, IllegalStateException {
     return getChannelProvider().getChannel(getOrBuildExecutor());
   }
 
@@ -98,7 +95,7 @@ public final ChannelProvider getChannelProvider() {
    * The Executor used for channels, retries, and bundling, retrieved using the executorProvider. If
    * no executor was set, a default executor will be instantiated.
    */
-  public final ScheduledExecutorService getOrBuildExecutor() throws OperationNotSupportedException {
+  public final ScheduledExecutorService getOrBuildExecutor() throws IllegalStateException {
     return getExecutorProvider().getExecutor();
   }
 
@@ -170,23 +167,23 @@ public boolean shouldAutoClose() {
      * Sets the executor to use for channels, retries, and bundling.
      *
      * If multiple Api objects will use this executor, shouldAutoClose must be set to false to
-     * prevent the ExecutorProvider from throwing an OperationNotSupportedException. See
+     * prevent the {@link ExecutorProvider} from throwing an {@link IllegalStateException}. See
      * {@link ExecutorProvider} for more details.
      */
     public Builder provideExecutorWith(
         final ScheduledExecutorService executor, final boolean shouldAutoClose) {
       executorProvider =
           new ExecutorProvider() {
-            private boolean executorProvided = false;
+            private volatile boolean executorProvided = false;
 
             @Override
-            public ScheduledExecutorService getExecutor() throws OperationNotSupportedException {
+            public ScheduledExecutorService getExecutor() throws IllegalStateException {
               if (executorProvided) {
                 if (shouldAutoClose) {
-                  throw new OperationNotSupportedException(
+                  throw new IllegalStateException(
                       "A fixed executor cannot be re-used when shouldAutoClose is set to true. "
-                          + "Try calling provideExecutorWith with shouldAutoClose set to false, or "
-                          + "using a channel created from a ConnectionSettings object.");
+                          + "Try calling provideExecutorWith with shouldAutoClose set to false "
+                          + "or using the default executor.");
                 }
               } else {
                 executorProvided = true;
@@ -209,7 +206,7 @@ public boolean shouldAutoClose() {
      * See class documentation for more details on channels.
      *
      * If multiple Api objects will use this channel, shouldAutoClose must be set to false to
-     * prevent the ChannelProvider from throwing an OperationNotSupportedException. See
+     * prevent the {@link ChannelProvider} from throwing an {@link IllegalStateException}. See
      * {@link ChannelProvider} for more details.
      */
     public Builder provideChannelWith(final ManagedChannel channel, final boolean shouldAutoClose) {
@@ -340,10 +337,10 @@ private ChannelProvider createChannelProvider(final ManagedChannel channel,
         private boolean channelProvided = false;
 
         @Override
-        public ManagedChannel getChannel(Executor executor) throws OperationNotSupportedException {
+        public ManagedChannel getChannel(Executor executor) throws IllegalStateException {
           if (channelProvided) {
             if (shouldAutoClose) {
-              throw new OperationNotSupportedException(
+              throw new IllegalStateException(
                   "A fixed channel cannot be re-used when shouldAutoClose is set to true. "
                       + "Try calling provideChannelWith with shouldAutoClose set to false, or "
                       + "using a channel created from a ConnectionSettings object.");