diff --git a/Rx.NET/Source/src/System.Reactive/Concurrency/LocalScheduler.TimerQueue.cs b/Rx.NET/Source/src/System.Reactive/Concurrency/LocalScheduler.TimerQueue.cs
index d09229aa87..f14670319b 100644
--- a/Rx.NET/Source/src/System.Reactive/Concurrency/LocalScheduler.TimerQueue.cs
+++ b/Rx.NET/Source/src/System.Reactive/Concurrency/LocalScheduler.TimerQueue.cs
@@ -428,7 +428,7 @@ private abstract class WorkItem : IComparable<WorkItem>, IDisposable
             private readonly SingleAssignmentDisposable _disposable;
             private int _hasRun;
 
-            public WorkItem(LocalScheduler scheduler, DateTimeOffset dueTime)
+            protected WorkItem(LocalScheduler scheduler, DateTimeOffset dueTime)
             {
                 Scheduler = scheduler;
                 DueTime = dueTime;
diff --git a/Rx.NET/Source/src/System.Reactive/Concurrency/Scheduler.Recursive.cs b/Rx.NET/Source/src/System.Reactive/Concurrency/Scheduler.Recursive.cs
index 24d343429d..af677d2216 100644
--- a/Rx.NET/Source/src/System.Reactive/Concurrency/Scheduler.Recursive.cs
+++ b/Rx.NET/Source/src/System.Reactive/Concurrency/Scheduler.Recursive.cs
@@ -177,7 +177,7 @@ private abstract class InvokeRecBaseState<TState> : IDisposable
 
             protected readonly CompositeDisposable group;
 
-            public InvokeRecBaseState(IScheduler scheduler)
+            protected InvokeRecBaseState(IScheduler scheduler)
             {
                 this.scheduler = scheduler;
                 group = new CompositeDisposable();
diff --git a/Rx.NET/Source/src/System.Reactive/Concurrency/SchedulerWrapper.cs b/Rx.NET/Source/src/System.Reactive/Concurrency/SchedulerWrapper.cs
index 4aac7c60bd..3e63b9646c 100644
--- a/Rx.NET/Source/src/System.Reactive/Concurrency/SchedulerWrapper.cs
+++ b/Rx.NET/Source/src/System.Reactive/Concurrency/SchedulerWrapper.cs
@@ -11,13 +11,13 @@ internal abstract class SchedulerWrapper : IScheduler, IServiceProvider
         protected readonly IScheduler _scheduler;
         private readonly ConditionalWeakTable<IScheduler, IScheduler> _cache;
 
-        public SchedulerWrapper(IScheduler scheduler)
+        protected SchedulerWrapper(IScheduler scheduler)
         {
             _scheduler = scheduler;
             _cache = new ConditionalWeakTable<IScheduler, IScheduler>();
         }
 
-        public SchedulerWrapper(IScheduler scheduler, ConditionalWeakTable<IScheduler, IScheduler> cache)
+        protected SchedulerWrapper(IScheduler scheduler, ConditionalWeakTable<IScheduler, IScheduler> cache)
         {
             _scheduler = scheduler;
             _cache = cache;
diff --git a/Rx.NET/Source/src/System.Reactive/Internal/ConcatSink.cs b/Rx.NET/Source/src/System.Reactive/Internal/ConcatSink.cs
index e5ed42e0bf..ee66f807a9 100644
--- a/Rx.NET/Source/src/System.Reactive/Internal/ConcatSink.cs
+++ b/Rx.NET/Source/src/System.Reactive/Internal/ConcatSink.cs
@@ -8,7 +8,7 @@ namespace System.Reactive
 {
     internal abstract class ConcatSink<TSource> : TailRecursiveSink<TSource>
     {
-        public ConcatSink(IObserver<TSource> observer)
+        protected ConcatSink(IObserver<TSource> observer)
             : base(observer)
         {
         }
diff --git a/Rx.NET/Source/src/System.Reactive/Internal/TailRecursiveSink.cs b/Rx.NET/Source/src/System.Reactive/Internal/TailRecursiveSink.cs
index 30603cf22a..b9b5090fd8 100644
--- a/Rx.NET/Source/src/System.Reactive/Internal/TailRecursiveSink.cs
+++ b/Rx.NET/Source/src/System.Reactive/Internal/TailRecursiveSink.cs
@@ -10,7 +10,7 @@ namespace System.Reactive
 {
     internal abstract class TailRecursiveSink<TSource> : IdentitySink<TSource>
     {
-        public TailRecursiveSink(IObserver<TSource> observer)
+        protected TailRecursiveSink(IObserver<TSource> observer)
             : base(observer)
         {
         }
diff --git a/Rx.NET/Source/src/System.Reactive/Linq/Observable/CombineLatest.cs b/Rx.NET/Source/src/System.Reactive/Linq/Observable/CombineLatest.cs
index 2cd24e89af..3a7df02801 100644
--- a/Rx.NET/Source/src/System.Reactive/Linq/Observable/CombineLatest.cs
+++ b/Rx.NET/Source/src/System.Reactive/Linq/Observable/CombineLatest.cs
@@ -236,7 +236,7 @@ internal abstract class CombineLatestSink<TResult> : IdentitySink<TResult>, ICom
         private readonly bool[] _hasValue;
         private readonly bool[] _isDone;
 
-        public CombineLatestSink(int arity, IObserver<TResult> observer)
+        protected CombineLatestSink(int arity, IObserver<TResult> observer)
             : base(observer)
         {
             _gate = new object();
diff --git a/Rx.NET/Source/src/System.Reactive/Linq/Observable/Delay.cs b/Rx.NET/Source/src/System.Reactive/Linq/Observable/Delay.cs
index 761a3f44b4..e8cb186b47 100644
--- a/Rx.NET/Source/src/System.Reactive/Linq/Observable/Delay.cs
+++ b/Rx.NET/Source/src/System.Reactive/Linq/Observable/Delay.cs
@@ -17,7 +17,7 @@ internal abstract class Base<TParent> : Producer<TSource, Base<TParent>._>
             protected readonly IObservable<TSource> _source;
             protected readonly IScheduler _scheduler;
 
-            public Base(IObservable<TSource> source, IScheduler scheduler)
+            protected Base(IObservable<TSource> source, IScheduler scheduler)
             {
                 _source = source;
                 _scheduler = scheduler;
@@ -28,7 +28,7 @@ internal abstract class _ : IdentitySink<TSource>
                 protected IStopwatch _watch;
                 protected IScheduler _scheduler;
 
-                public _(TParent parent, IObserver<TSource> observer)
+                protected _(TParent parent, IObserver<TSource> observer)
                     : base(observer)
                 {
                     _scheduler = parent._scheduler;
@@ -51,7 +51,7 @@ internal abstract class S : _
                 protected readonly object _gate = new object();
                 protected IDisposable _cancelable;
 
-                public S(TParent parent, IObserver<TSource> observer)
+                protected S(TParent parent, IObserver<TSource> observer)
                     : base(parent, observer)
                 {
                 }
@@ -258,7 +258,7 @@ protected abstract class L : _
                 protected IDisposable _cancelable;
                 private readonly SemaphoreSlim _evt = new SemaphoreSlim(0);
 
-                public L(TParent parent, IObserver<TSource> observer)
+                protected L(TParent parent, IObserver<TSource> observer)
                     : base(parent, observer)
                 {
                 }
@@ -586,7 +586,7 @@ internal abstract class Base<TParent> : Producer<TSource, Base<TParent>._>
         {
             protected readonly IObservable<TSource> _source;
 
-            public Base(IObservable<TSource> source)
+            protected Base(IObservable<TSource> source)
             {
                 _source = source;
             }
@@ -598,7 +598,7 @@ internal abstract class _ : IdentitySink<TSource>
 
                 private readonly Func<TSource, IObservable<TDelay>> _delaySelector;
 
-                public _(Func<TSource, IObservable<TDelay>> delaySelector, IObserver<TSource> observer)
+                protected _(Func<TSource, IObservable<TDelay>> delaySelector, IObserver<TSource> observer)
                     : base(observer)
                 {
                     _delaySelector = delaySelector;
diff --git a/Rx.NET/Source/src/System.Reactive/Linq/Observable/DelaySubscription.cs b/Rx.NET/Source/src/System.Reactive/Linq/Observable/DelaySubscription.cs
index 79a30ff8f7..342b8bc8bb 100644
--- a/Rx.NET/Source/src/System.Reactive/Linq/Observable/DelaySubscription.cs
+++ b/Rx.NET/Source/src/System.Reactive/Linq/Observable/DelaySubscription.cs
@@ -11,7 +11,7 @@ internal abstract class DelaySubscription<TSource> : Producer<TSource, DelaySubs
         private readonly IObservable<TSource> _source;
         private readonly IScheduler _scheduler;
 
-        public DelaySubscription(IObservable<TSource> source, IScheduler scheduler)
+        protected DelaySubscription(IObservable<TSource> source, IScheduler scheduler)
         {
             _source = source;
             _scheduler = scheduler;
diff --git a/Rx.NET/Source/src/System.Reactive/Linq/Observable/FromEvent.cs b/Rx.NET/Source/src/System.Reactive/Linq/Observable/FromEvent.cs
index 3ae2d740f4..0538b76897 100644
--- a/Rx.NET/Source/src/System.Reactive/Linq/Observable/FromEvent.cs
+++ b/Rx.NET/Source/src/System.Reactive/Linq/Observable/FromEvent.cs
@@ -195,7 +195,7 @@ internal abstract class EventProducer<TDelegate, TArgs> : BasicProducer<TArgs>
         private readonly IScheduler _scheduler;
         private readonly object _gate;
 
-        public EventProducer(IScheduler scheduler)
+        protected EventProducer(IScheduler scheduler)
         {
             _scheduler = scheduler;
             _gate = new object();
@@ -358,7 +358,7 @@ internal abstract class ClassicEventProducer<TDelegate, TArgs> : EventProducer<T
         private readonly Action<TDelegate> _addHandler;
         private readonly Action<TDelegate> _removeHandler;
 
-        public ClassicEventProducer(Action<TDelegate> addHandler, Action<TDelegate> removeHandler, IScheduler scheduler)
+        protected ClassicEventProducer(Action<TDelegate> addHandler, Action<TDelegate> removeHandler, IScheduler scheduler)
             : base(scheduler)
         {
             _addHandler = addHandler;
diff --git a/Rx.NET/Source/src/System.Reactive/Linq/Observable/Max.cs b/Rx.NET/Source/src/System.Reactive/Linq/Observable/Max.cs
index e442333e29..47cbd0721f 100644
--- a/Rx.NET/Source/src/System.Reactive/Linq/Observable/Max.cs
+++ b/Rx.NET/Source/src/System.Reactive/Linq/Observable/Max.cs
@@ -25,7 +25,7 @@ internal abstract class _ : IdentitySink<TSource>
         {
             protected readonly IComparer<TSource> _comparer;
 
-            public _(IComparer<TSource> comparer, IObserver<TSource> observer)
+            protected _(IComparer<TSource> comparer, IObserver<TSource> observer)
                 : base(observer)
             {
                 _comparer = comparer;
diff --git a/Rx.NET/Source/src/System.Reactive/Linq/Observable/Min.cs b/Rx.NET/Source/src/System.Reactive/Linq/Observable/Min.cs
index 4656910c8a..92d70de11b 100644
--- a/Rx.NET/Source/src/System.Reactive/Linq/Observable/Min.cs
+++ b/Rx.NET/Source/src/System.Reactive/Linq/Observable/Min.cs
@@ -25,7 +25,7 @@ internal abstract class _ : IdentitySink<TSource>
         {
             protected readonly IComparer<TSource> _comparer;
 
-            public _(IComparer<TSource> comparer, IObserver<TSource> observer)
+            protected _(IComparer<TSource> comparer, IObserver<TSource> observer)
                 : base(observer)
             {
                 _comparer = comparer;
diff --git a/Rx.NET/Source/src/System.Reactive/Linq/Observable/PushToPullAdapter.cs b/Rx.NET/Source/src/System.Reactive/Linq/Observable/PushToPullAdapter.cs
index de2731b5ee..1646461658 100644
--- a/Rx.NET/Source/src/System.Reactive/Linq/Observable/PushToPullAdapter.cs
+++ b/Rx.NET/Source/src/System.Reactive/Linq/Observable/PushToPullAdapter.cs
@@ -12,7 +12,7 @@ internal abstract class PushToPullAdapter<TSource, TResult> : IEnumerable<TResul
     {
         private readonly IObservable<TSource> _source;
 
-        public PushToPullAdapter(IObservable<TSource> source)
+        protected PushToPullAdapter(IObservable<TSource> source)
         {
             _source = source;
         }
diff --git a/Rx.NET/Source/src/System.Reactive/Linq/Observable/Timer.cs b/Rx.NET/Source/src/System.Reactive/Linq/Observable/Timer.cs
index 40633ad30e..61a3280cb3 100644
--- a/Rx.NET/Source/src/System.Reactive/Linq/Observable/Timer.cs
+++ b/Rx.NET/Source/src/System.Reactive/Linq/Observable/Timer.cs
@@ -14,7 +14,7 @@ internal abstract class Single : Producer<long, Single._>
         {
             private readonly IScheduler _scheduler;
 
-            public Single(IScheduler scheduler)
+            protected Single(IScheduler scheduler)
             {
                 _scheduler = scheduler;
             }
@@ -80,7 +80,7 @@ internal abstract class Periodic : Producer<long, Periodic._>
             private readonly TimeSpan _period;
             private readonly IScheduler _scheduler;
 
-            public Periodic(TimeSpan period, IScheduler scheduler)
+            protected Periodic(TimeSpan period, IScheduler scheduler)
             {
                 _period = period;
                 _scheduler = scheduler;
diff --git a/Rx.NET/Source/src/System.Reactive/Linq/Observable/Zip.cs b/Rx.NET/Source/src/System.Reactive/Linq/Observable/Zip.cs
index 284aa0e41d..df81edce74 100644
--- a/Rx.NET/Source/src/System.Reactive/Linq/Observable/Zip.cs
+++ b/Rx.NET/Source/src/System.Reactive/Linq/Observable/Zip.cs
@@ -390,7 +390,7 @@ internal abstract class ZipSink<TResult> : IdentitySink<TResult>, IZip
         private readonly ICollection[] _queues;
         private readonly bool[] _isDone;
 
-        public ZipSink(int arity, IObserver<TResult> observer)
+        protected ZipSink(int arity, IObserver<TResult> observer)
             : base(observer)
         {
             _gate = new object();
diff --git a/Rx.NET/Source/src/System.Reactive/Subjects/ReplaySubject.cs b/Rx.NET/Source/src/System.Reactive/Subjects/ReplaySubject.cs
index 150447dfa7..be12c756a9 100644
--- a/Rx.NET/Source/src/System.Reactive/Subjects/ReplaySubject.cs
+++ b/Rx.NET/Source/src/System.Reactive/Subjects/ReplaySubject.cs
@@ -229,7 +229,7 @@ private abstract class ReplayBase : SubjectBase<T>
             private Exception _error;
             private bool _isDisposed;
 
-            public ReplayBase()
+            protected ReplayBase()
             {
                 _observers = ImmutableList<IScheduledObserver<T>>.Empty;