diff --git a/src/main/java/io/reactivex/internal/operators/flowable/FlowableAmb.java b/src/main/java/io/reactivex/internal/operators/flowable/FlowableAmb.java
index 5af4200aa9..3523fbcd29 100644
--- a/src/main/java/io/reactivex/internal/operators/flowable/FlowableAmb.java
+++ b/src/main/java/io/reactivex/internal/operators/flowable/FlowableAmb.java
@@ -15,6 +15,7 @@
 
 import java.util.concurrent.atomic.*;
 
+import io.reactivex.exceptions.Exceptions;
 import org.reactivestreams.*;
 
 import io.reactivex.Flowable;
@@ -38,13 +39,23 @@ public void subscribeActual(Subscriber<? super T> s) {
         int count = 0;
         if (sources == null) {
             sources = new Publisher[8];
-            for (Publisher<? extends T> p : sourcesIterable) {
-                if (count == sources.length) {
-                    Publisher<? extends T>[] b = new Publisher[count + (count >> 2)];
-                    System.arraycopy(sources, 0, b, 0, count);
-                    sources = b;
+            try {
+                for (Publisher<? extends T> p : sourcesIterable) {
+                    if (p == null) {
+                        EmptySubscription.error(new NullPointerException("One of the sources is null"), s);
+                        return;
+                    }
+                    if (count == sources.length) {
+                        Publisher<? extends T>[] b = new Publisher[count + (count >> 2)];
+                        System.arraycopy(sources, 0, b, 0, count);
+                        sources = b;
+                    }
+                    sources[count++] = p;
                 }
-                sources[count++] = p;
+            } catch (Throwable e) {
+                Exceptions.throwIfFatal(e);
+                EmptySubscription.error(e, s);
+                return;
             }
         } else {
             count = sources.length;
diff --git a/src/main/java/io/reactivex/internal/operators/observable/ObservableAmb.java b/src/main/java/io/reactivex/internal/operators/observable/ObservableAmb.java
index e4c4ef2c2e..078268e5f6 100644
--- a/src/main/java/io/reactivex/internal/operators/observable/ObservableAmb.java
+++ b/src/main/java/io/reactivex/internal/operators/observable/ObservableAmb.java
@@ -17,6 +17,7 @@
 
 import io.reactivex.*;
 import io.reactivex.disposables.Disposable;
+import io.reactivex.exceptions.Exceptions;
 import io.reactivex.internal.disposables.*;
 import io.reactivex.plugins.RxJavaPlugins;
 
@@ -36,13 +37,23 @@ public void subscribeActual(Observer<? super T> s) {
         int count = 0;
         if (sources == null) {
             sources = new Observable[8];
-            for (ObservableSource<? extends T> p : sourcesIterable) {
-                if (count == sources.length) {
-                    ObservableSource<? extends T>[] b = new ObservableSource[count + (count >> 2)];
-                    System.arraycopy(sources, 0, b, 0, count);
-                    sources = b;
+            try {
+                for (ObservableSource<? extends T> p : sourcesIterable) {
+                    if (p == null) {
+                        EmptyDisposable.error(new NullPointerException("One of the sources is null"), s);
+                        return;
+                    }
+                    if (count == sources.length) {
+                        ObservableSource<? extends T>[] b = new ObservableSource[count + (count >> 2)];
+                        System.arraycopy(sources, 0, b, 0, count);
+                        sources = b;
+                    }
+                    sources[count++] = p;
                 }
-                sources[count++] = p;
+            } catch (Throwable e) {
+                Exceptions.throwIfFatal(e);
+                EmptyDisposable.error(e, s);
+                return;
             }
         } else {
             count = sources.length;
diff --git a/src/test/java/io/reactivex/flowable/FlowableNullTests.java b/src/test/java/io/reactivex/flowable/FlowableNullTests.java
index af2f83f67c..b4191f6cd0 100644
--- a/src/test/java/io/reactivex/flowable/FlowableNullTests.java
+++ b/src/test/java/io/reactivex/flowable/FlowableNullTests.java
@@ -55,20 +55,22 @@ public void ambIterableNull() {
         Flowable.amb((Iterable<Publisher<Object>>)null);
     }
 
-    @Test(expected = NullPointerException.class)
+    @Test
     public void ambIterableIteratorNull() {
         Flowable.amb(new Iterable<Publisher<Object>>() {
             @Override
             public Iterator<Publisher<Object>> iterator() {
                 return null;
             }
-        }).blockingLast();
+        }).test().assertError(NullPointerException.class);
     }
 
     @SuppressWarnings("unchecked")
-    @Test(expected = NullPointerException.class)
+    @Test
     public void ambIterableOneIsNull() {
-        Flowable.amb(Arrays.asList(Flowable.never(), null)).blockingLast();
+        Flowable.amb(Arrays.asList(Flowable.never(), null))
+                .test()
+                .assertError(NullPointerException.class);
     }
 
     @Test(expected = NullPointerException.class)
diff --git a/src/test/java/io/reactivex/observable/ObservableNullTests.java b/src/test/java/io/reactivex/observable/ObservableNullTests.java
index 2f43c85452..2dea75f9db 100644
--- a/src/test/java/io/reactivex/observable/ObservableNullTests.java
+++ b/src/test/java/io/reactivex/observable/ObservableNullTests.java
@@ -56,20 +56,22 @@ public void ambIterableNull() {
         Observable.amb((Iterable<Observable<Object>>)null);
     }
 
-    @Test(expected = NullPointerException.class)
+    @Test
     public void ambIterableIteratorNull() {
         Observable.amb(new Iterable<Observable<Object>>() {
             @Override
             public Iterator<Observable<Object>> iterator() {
                 return null;
             }
-        }).blockingLast();
+        }).test().assertError(NullPointerException.class);
     }
 
     @SuppressWarnings("unchecked")
-    @Test(expected = NullPointerException.class)
+    @Test
     public void ambIterableOneIsNull() {
-        Observable.amb(Arrays.asList(Observable.never(), null)).blockingLast();
+        Observable.amb(Arrays.asList(Observable.never(), null))
+                .test()
+                .assertError(NullPointerException.class);
     }
 
     @Test(expected = NullPointerException.class)