diff --git a/src/main/java/io/reactivex/internal/operators/observable/ObservableConcatMap.java b/src/main/java/io/reactivex/internal/operators/observable/ObservableConcatMap.java
index b3cb5ff531..8e66db0bdc 100644
--- a/src/main/java/io/reactivex/internal/operators/observable/ObservableConcatMap.java
+++ b/src/main/java/io/reactivex/internal/operators/observable/ObservableConcatMap.java
@@ -13,7 +13,7 @@
 package io.reactivex.internal.operators.observable;
 
 import java.util.concurrent.Callable;
-import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.atomic.*;
 
 import io.reactivex.*;
 import io.reactivex.disposables.Disposable;
@@ -59,9 +59,8 @@ static final class SourceObserver<T, U> extends AtomicInteger implements Observe
 
         private static final long serialVersionUID = 8828587559905699186L;
         final Observer<? super U> actual;
-        final SequentialDisposable sa;
         final Function<? super T, ? extends ObservableSource<? extends U>> mapper;
-        final Observer<U> inner;
+        final InnerObserver<U> inner;
         final int bufferSize;
 
         SimpleQueue<T> queue;
@@ -82,7 +81,6 @@ static final class SourceObserver<T, U> extends AtomicInteger implements Observe
             this.mapper = mapper;
             this.bufferSize = bufferSize;
             this.inner = new InnerObserver<U>(actual, this);
-            this.sa = new SequentialDisposable();
         }
         @Override
         public void onSubscribe(Disposable s) {
@@ -161,7 +159,7 @@ public boolean isDisposed() {
         @Override
         public void dispose() {
             disposed = true;
-            sa.dispose();
+            inner.dispose();
             s.dispose();
 
             if (getAndIncrement() == 0) {
@@ -169,10 +167,6 @@ public void dispose() {
             }
         }
 
-        void innerSubscribe(Disposable s) {
-            sa.update(s);
-        }
-
         void drain() {
             if (getAndIncrement() != 0) {
                 return;
@@ -231,7 +225,10 @@ void drain() {
             }
         }
 
-        static final class InnerObserver<U> implements Observer<U> {
+        static final class InnerObserver<U> extends AtomicReference<Disposable> implements Observer<U> {
+
+            private static final long serialVersionUID = -7449079488798789337L;
+
             final Observer<? super U> actual;
             final SourceObserver<?, ?> parent;
 
@@ -242,7 +239,7 @@ static final class InnerObserver<U> implements Observer<U> {
 
             @Override
             public void onSubscribe(Disposable s) {
-                parent.innerSubscribe(s);
+                DisposableHelper.set(this, s);
             }
 
             @Override
@@ -258,6 +255,10 @@ public void onError(Throwable t) {
             public void onComplete() {
                 parent.innerComplete();
             }
+
+            void dispose() {
+                DisposableHelper.dispose(this);
+            }
         }
     }
 
@@ -278,8 +279,6 @@ static final class ConcatMapDelayErrorObserver<T, R>
 
         final DelayErrorInnerObserver<R> observer;
 
-        final SequentialDisposable arbiter;
-
         final boolean tillTheEnd;
 
         SimpleQueue<T> queue;
@@ -303,7 +302,6 @@ static final class ConcatMapDelayErrorObserver<T, R>
             this.tillTheEnd = tillTheEnd;
             this.error = new AtomicThrowable();
             this.observer = new DelayErrorInnerObserver<R>(actual, this);
-            this.arbiter = new SequentialDisposable();
         }
 
         @Override
@@ -375,7 +373,7 @@ public boolean isDisposed() {
         public void dispose() {
             cancelled = true;
             d.dispose();
-            arbiter.dispose();
+            observer.dispose();
         }
 
         @SuppressWarnings("unchecked")
@@ -479,7 +477,9 @@ void drain() {
             }
         }
 
-        static final class DelayErrorInnerObserver<R> implements Observer<R> {
+        static final class DelayErrorInnerObserver<R> extends AtomicReference<Disposable> implements Observer<R> {
+
+            private static final long serialVersionUID = 2620149119579502636L;
 
             final Observer<? super R> actual;
 
@@ -492,7 +492,7 @@ static final class DelayErrorInnerObserver<R> implements Observer<R> {
 
             @Override
             public void onSubscribe(Disposable d) {
-                parent.arbiter.replace(d);
+                DisposableHelper.replace(this, d);
             }
 
             @Override
@@ -520,6 +520,10 @@ public void onComplete() {
                 p.active = false;
                 p.drain();
             }
+
+            void dispose() {
+                DisposableHelper.dispose(this);
+            }
         }
     }
 }
diff --git a/src/main/java/io/reactivex/internal/operators/observable/ObservableConcatMapCompletable.java b/src/main/java/io/reactivex/internal/operators/observable/ObservableConcatMapCompletable.java
index 909ba644f3..b53de7cde7 100644
--- a/src/main/java/io/reactivex/internal/operators/observable/ObservableConcatMapCompletable.java
+++ b/src/main/java/io/reactivex/internal/operators/observable/ObservableConcatMapCompletable.java
@@ -12,20 +12,18 @@
  */
 package io.reactivex.internal.operators.observable;
 
+import java.util.concurrent.atomic.*;
+
 import io.reactivex.*;
 import io.reactivex.disposables.Disposable;
 import io.reactivex.exceptions.Exceptions;
 import io.reactivex.functions.Function;
 import io.reactivex.internal.disposables.DisposableHelper;
-import io.reactivex.internal.disposables.SequentialDisposable;
 import io.reactivex.internal.functions.ObjectHelper;
-import io.reactivex.internal.fuseable.QueueDisposable;
-import io.reactivex.internal.fuseable.SimpleQueue;
+import io.reactivex.internal.fuseable.*;
 import io.reactivex.internal.queue.SpscLinkedArrayQueue;
 import io.reactivex.plugins.RxJavaPlugins;
 
-import java.util.concurrent.atomic.AtomicInteger;
-
 public final class ObservableConcatMapCompletable<T> extends Completable {
 
     final ObservableSource<T> source;
@@ -47,9 +45,8 @@ static final class SourceObserver<T> extends AtomicInteger implements Observer<T
 
         private static final long serialVersionUID = 6893587405571511048L;
         final CompletableObserver actual;
-        final SequentialDisposable sa;
         final Function<? super T, ? extends CompletableSource> mapper;
-        final CompletableObserver inner;
+        final InnerObserver inner;
         final int bufferSize;
 
         SimpleQueue<T> queue;
@@ -70,7 +67,6 @@ static final class SourceObserver<T> extends AtomicInteger implements Observer<T
             this.mapper = mapper;
             this.bufferSize = bufferSize;
             this.inner = new InnerObserver(actual, this);
-            this.sa = new SequentialDisposable();
         }
         @Override
         public void onSubscribe(Disposable s) {
@@ -149,7 +145,7 @@ public boolean isDisposed() {
         @Override
         public void dispose() {
             disposed = true;
-            sa.dispose();
+            inner.dispose();
             s.dispose();
 
             if (getAndIncrement() == 0) {
@@ -157,10 +153,6 @@ public void dispose() {
             }
         }
 
-        void innerSubscribe(Disposable s) {
-            sa.update(s);
-        }
-
         void drain() {
             if (getAndIncrement() != 0) {
                 return;
@@ -219,7 +211,8 @@ void drain() {
             }
         }
 
-        static final class InnerObserver implements CompletableObserver {
+        static final class InnerObserver extends AtomicReference<Disposable> implements CompletableObserver {
+            private static final long serialVersionUID = -5987419458390772447L;
             final CompletableObserver actual;
             final SourceObserver<?> parent;
 
@@ -230,7 +223,7 @@ static final class InnerObserver implements CompletableObserver {
 
             @Override
             public void onSubscribe(Disposable s) {
-                parent.innerSubscribe(s);
+                DisposableHelper.set(this, s);
             }
 
             @Override
@@ -242,6 +235,10 @@ public void onError(Throwable t) {
             public void onComplete() {
                 parent.innerComplete();
             }
+
+            void dispose() {
+                DisposableHelper.dispose(this);
+            }
         }
     }
 }