diff --git a/src/main/java/io/reactivex/internal/operators/flowable/FlowableGenerate.java b/src/main/java/io/reactivex/internal/operators/flowable/FlowableGenerate.java
index 0520670a93..5b7a2a796a 100644
--- a/src/main/java/io/reactivex/internal/operators/flowable/FlowableGenerate.java
+++ b/src/main/java/io/reactivex/internal/operators/flowable/FlowableGenerate.java
@@ -68,6 +68,8 @@ static final class GeneratorSubscription<T, S>
 
         boolean terminate;
 
+        boolean hasNext;
+
         GeneratorSubscription(Subscriber<? super T> actual,
                 BiFunction<S, ? super Emitter<T>, S> generator,
                 Consumer<? super S> disposeState, S initialState) {
@@ -96,21 +98,27 @@ public void request(long n) {
                 while (e != n) {
 
                     if (cancelled) {
+                        state = null;
                         dispose(s);
                         return;
                     }
 
+                    hasNext = false;
+
                     try {
                         s = f.apply(s, this);
                     } catch (Throwable ex) {
                         Exceptions.throwIfFatal(ex);
                         cancelled = true;
-                        actual.onError(ex);
+                        state = null;
+                        onError(ex);
+                        dispose(s);
                         return;
                     }
 
                     if (terminate) {
                         cancelled = true;
+                        state = null;
                         dispose(s);
                         return;
                     }
@@ -146,33 +154,48 @@ public void cancel() {
 
                 // if there are no running requests, just dispose the state
                 if (BackpressureHelper.add(this, 1) == 0) {
-                    dispose(state);
+                    S s = state;
+                    state = null;
+                    dispose(s);
                 }
             }
         }
 
         @Override
         public void onNext(T t) {
-            if (t == null) {
-                onError(new NullPointerException("onNext called with null. Null values are generally not allowed in 2.x operators and sources."));
-                return;
+            if (!terminate) {
+                if (hasNext) {
+                    onError(new IllegalStateException("onNext already called in this generate turn"));
+                } else {
+                    if (t == null) {
+                        onError(new NullPointerException("onNext called with null. Null values are generally not allowed in 2.x operators and sources."));
+                    } else {
+                        hasNext = true;
+                        actual.onNext(t);
+                    }
+                }
             }
-            actual.onNext(t);
         }
 
         @Override
         public void onError(Throwable t) {
-            if (t == null) {
-                t = new NullPointerException("onError called with null. Null values are generally not allowed in 2.x operators and sources.");
+            if (terminate) {
+                RxJavaPlugins.onError(t);
+            } else {
+                if (t == null) {
+                    t = new NullPointerException("onError called with null. Null values are generally not allowed in 2.x operators and sources.");
+                }
+                terminate = true;
+                actual.onError(t);
             }
-            terminate = true;
-            actual.onError(t);
         }
 
         @Override
         public void onComplete() {
-            terminate = true;
-            actual.onComplete();
+            if (!terminate) {
+                terminate = true;
+                actual.onComplete();
+            }
         }
     }
 }
diff --git a/src/main/java/io/reactivex/internal/operators/observable/ObservableGenerate.java b/src/main/java/io/reactivex/internal/operators/observable/ObservableGenerate.java
index f5bcc6516d..50a38cf29f 100644
--- a/src/main/java/io/reactivex/internal/operators/observable/ObservableGenerate.java
+++ b/src/main/java/io/reactivex/internal/operators/observable/ObservableGenerate.java
@@ -64,6 +64,8 @@ static final class GeneratorDisposable<T, S>
 
         boolean terminate;
 
+        boolean hasNext;
+
         GeneratorDisposable(Observer<? super T> actual,
                 BiFunction<S, ? super Emitter<T>, S> generator,
                 Consumer<? super S> disposeState, S initialState) {
@@ -92,13 +94,16 @@ public void run() {
                     return;
                 }
 
+                hasNext = false;
+
                 try {
                     s = f.apply(s, this);
                 } catch (Throwable ex) {
                     Exceptions.throwIfFatal(ex);
                     state = null;
                     cancelled = true;
-                    actual.onError(ex);
+                    onError(ex);
+                    dispose(s);
                     return;
                 }
 
@@ -131,28 +136,42 @@ public boolean isDisposed() {
             return cancelled;
         }
 
+
         @Override
         public void onNext(T t) {
-            if (t == null) {
-                onError(new NullPointerException("onNext called with null. Null values are generally not allowed in 2.x operators and sources."));
-                return;
+            if (!terminate) {
+                if (hasNext) {
+                    onError(new IllegalStateException("onNext already called in this generate turn"));
+                } else {
+                    if (t == null) {
+                        onError(new NullPointerException("onNext called with null. Null values are generally not allowed in 2.x operators and sources."));
+                    } else {
+                        hasNext = true;
+                        actual.onNext(t);
+                    }
+                }
             }
-            actual.onNext(t);
         }
 
         @Override
         public void onError(Throwable t) {
-            if (t == null) {
-                t = new NullPointerException("onError called with null. Null values are generally not allowed in 2.x operators and sources.");
+            if (terminate) {
+                RxJavaPlugins.onError(t);
+            } else {
+                if (t == null) {
+                    t = new NullPointerException("onError called with null. Null values are generally not allowed in 2.x operators and sources.");
+                }
+                terminate = true;
+                actual.onError(t);
             }
-            terminate = true;
-            actual.onError(t);
         }
 
         @Override
         public void onComplete() {
-            terminate = true;
-            actual.onComplete();
+            if (!terminate) {
+                terminate = true;
+                actual.onComplete();
+            }
         }
     }
 }
diff --git a/src/test/java/io/reactivex/internal/operators/flowable/FlowableGenerateTest.java b/src/test/java/io/reactivex/internal/operators/flowable/FlowableGenerateTest.java
index 6166c8f38d..aaf268fb5e 100644
--- a/src/test/java/io/reactivex/internal/operators/flowable/FlowableGenerateTest.java
+++ b/src/test/java/io/reactivex/internal/operators/flowable/FlowableGenerateTest.java
@@ -236,4 +236,50 @@ public void run() {
             ts.assertValueCount(1000);
         }
     }
+
+    @Test
+    public void multipleOnNext() {
+        Flowable.generate(new Consumer<Emitter<Object>>() {
+            @Override
+            public void accept(Emitter<Object> e) throws Exception {
+                e.onNext(1);
+                e.onNext(2);
+            }
+        })
+        .test(1)
+        .assertFailure(IllegalStateException.class, 1);
+    }
+
+    @Test
+    public void multipleOnError() {
+        List<Throwable> errors = TestHelper.trackPluginErrors();
+        try {
+            Flowable.generate(new Consumer<Emitter<Object>>() {
+                @Override
+                public void accept(Emitter<Object> e) throws Exception {
+                    e.onError(new TestException("First"));
+                    e.onError(new TestException("Second"));
+                }
+            })
+            .test(1)
+            .assertFailure(TestException.class);
+
+            TestHelper.assertError(errors, 0, TestException.class, "Second");
+        } finally {
+            RxJavaPlugins.reset();
+        }
+    }
+
+    @Test
+    public void multipleOnComplete() {
+        Flowable.generate(new Consumer<Emitter<Object>>() {
+            @Override
+            public void accept(Emitter<Object> e) throws Exception {
+                e.onComplete();
+                e.onComplete();
+            }
+        })
+        .test(1)
+        .assertResult();
+    }
 }
diff --git a/src/test/java/io/reactivex/internal/operators/observable/ObservableGenerateTest.java b/src/test/java/io/reactivex/internal/operators/observable/ObservableGenerateTest.java
index 7235eb3f13..de4880b579 100644
--- a/src/test/java/io/reactivex/internal/operators/observable/ObservableGenerateTest.java
+++ b/src/test/java/io/reactivex/internal/operators/observable/ObservableGenerateTest.java
@@ -147,4 +147,50 @@ public void accept(Integer s, Emitter<Object> e) throws Exception {
 
         assertEquals(0, call[0]);
     }
+
+    @Test
+    public void multipleOnNext() {
+        Observable.generate(new Consumer<Emitter<Object>>() {
+            @Override
+            public void accept(Emitter<Object> e) throws Exception {
+                e.onNext(1);
+                e.onNext(2);
+            }
+        })
+        .test()
+        .assertFailure(IllegalStateException.class, 1);
+    }
+
+    @Test
+    public void multipleOnError() {
+        List<Throwable> errors = TestHelper.trackPluginErrors();
+        try {
+            Observable.generate(new Consumer<Emitter<Object>>() {
+                @Override
+                public void accept(Emitter<Object> e) throws Exception {
+                    e.onError(new TestException("First"));
+                    e.onError(new TestException("Second"));
+                }
+            })
+            .test()
+            .assertFailure(TestException.class);
+
+            TestHelper.assertError(errors, 0, TestException.class, "Second");
+        } finally {
+            RxJavaPlugins.reset();
+        }
+    }
+
+    @Test
+    public void multipleOnComplete() {
+        Observable.generate(new Consumer<Emitter<Object>>() {
+            @Override
+            public void accept(Emitter<Object> e) throws Exception {
+                e.onComplete();
+                e.onComplete();
+            }
+        })
+        .test()
+        .assertResult();
+    }
 }