diff --git a/SSignalKit/SSignal+Meta.m b/SSignalKit/SSignal+Meta.m
index 0adc4846ab..16ccfd7069 100644
--- a/SSignalKit/SSignal+Meta.m
+++ b/SSignalKit/SSignal+Meta.m
@@ -5,41 +5,114 @@
 #import "SSignal+Mapping.h"
 #import "SAtomic.h"
 
+#import <libkern/OSAtomic.h>
+
+@interface SSignalSwitchToLatestState : NSObject <SDisposable>
+{
+    OSSpinLock _lock;
+    bool _didSwitch;
+    bool _terminated;
+    
+    id<SDisposable> _disposable;
+    SMetaDisposable *_currentDisposable;
+    SSubscriber *_subscriber;
+}
+
+@end
+
+@implementation SSignalSwitchToLatestState
+
+- (instancetype)initWithSubscriber:(SSubscriber *)subscriber
+{
+    self = [super init];
+    if (self != nil)
+    {
+        _subscriber = subscriber;
+        _currentDisposable = [[SMetaDisposable alloc] init];
+    }
+    return self;
+}
+
+- (void)beginWithDisposable:(id<SDisposable>)disposable
+{
+    _disposable = disposable;
+}
+
+- (void)switchToSignal:(SSignal *)signal
+{
+    OSSpinLockLock(&_lock);
+    _didSwitch = true;
+    OSSpinLockUnlock(&_lock);
+    
+    id<SDisposable> disposable = [signal startWithNext:^(id next)
+    {
+        [_subscriber putNext:next];
+    } error:^(id error)
+    {
+        [_subscriber putError:error];
+    } completed:^
+    {
+        OSSpinLockLock(&_lock);
+        _didSwitch = false;
+        OSSpinLockUnlock(&_lock);
+        
+        [self maybeComplete];
+    }];
+    
+    [_currentDisposable setDisposable:disposable];
+}
+
+- (void)maybeComplete
+{
+    bool terminated = false;
+    OSSpinLockLock(&_lock);
+    terminated = _terminated;
+    OSSpinLockUnlock(&_lock);
+    
+    if (terminated)
+        [_subscriber putCompletion];
+}
+
+- (void)beginCompletion
+{
+    bool didSwitch = false;
+    OSSpinLockLock(&_lock);
+    didSwitch = _didSwitch;
+    _terminated = true;
+    OSSpinLockUnlock(&_lock);
+    
+    if (!didSwitch)
+        [_subscriber putCompletion];
+}
+
+- (void)dispose
+{
+    [_disposable dispose];
+    [_currentDisposable dispose];
+}
+
+@end
+
 @implementation SSignal (Meta)
 
 - (SSignal *)switchToLatest
 {
     return [[SSignal alloc] initWithGenerator:^id<SDisposable> (SSubscriber *subscriber)
     {
-        SDisposableSet *compositeDisposable = [[SDisposableSet alloc] init];
+        SSignalSwitchToLatestState *state = [[SSignalSwitchToLatestState alloc] initWithSubscriber:subscriber];
         
-        SMetaDisposable *currentDisposable = [[SMetaDisposable alloc] init];
-        [compositeDisposable add:currentDisposable];
-        
-        SAtomic *didProduceNext = [[SAtomic alloc] initWithValue:nil];
-        [compositeDisposable add:[self startWithNext:^(SSignal *next)
+        [state beginWithDisposable:[self startWithNext:^(id next)
         {
-            [didProduceNext swap:@1];
-            [currentDisposable setDisposable:[next startWithNext:^(id next)
-            {
-                [subscriber putNext:next];
-            } error:^(id error)
-            {
-                [subscriber putError:error];
-            } completed:^
-            {
-                [subscriber putCompletion];
-            }]];
+            [state switchToSignal:next];
         } error:^(id error)
         {
             [subscriber putError:error];
         } completed:^
         {
-            if ([didProduceNext swap:@1] == NULL)
-                [subscriber putCompletion];
+            [state beginCompletion];
         }]];
         
-        return compositeDisposable;
+        return state;
     }];
 }
 
diff --git a/SSignalKit/SSubscriber.m b/SSignalKit/SSubscriber.m
index ef5979d5db..9c0e26cb5a 100644
--- a/SSignalKit/SSubscriber.m
+++ b/SSignalKit/SSubscriber.m
@@ -27,7 +27,10 @@
 
 - (void)_assignDisposable:(id<SDisposable>)disposable
 {
-    _disposable = disposable;
+    if (_terminated)
+        [disposable dispose];
+    else
+        _disposable = disposable;
 }
 
 - (void)_markTerminatedWithoutDisposal
diff --git a/SSignalKitTests/SSignalBasicTests.m b/SSignalKitTests/SSignalBasicTests.m
index abe09c87a1..e4d871b348 100644
--- a/SSignalKitTests/SSignalBasicTests.m
+++ b/SSignalKitTests/SSignalBasicTests.m
@@ -179,15 +179,15 @@
         SSignal *signal = [[[SSignal alloc] initWithGenerator:^id<SDisposable>(SSubscriber *subscriber)
         {
             [subscriber putNext:@1];
-            [object description];
+            __unused id a0 = [object description];
             return [[SBlockDisposable alloc] initWithBlock:^
             {
-                [object description];
+                __unused id a1 = [object description];
                 disposed = true;
             }];
         }] _mapInplace:^id(id value)
         {
-            [object description];
+            __unused id a1 = [object description];
             return @([value intValue] * 2);
         }];
         
@@ -242,4 +242,165 @@
     XCTAssertFalse(generated);
 }
 
+- (void)testThen
+{
+    __block bool generatedFirst = false;
+    __block bool disposedFirst = false;
+    __block bool generatedSecond = false;
+    __block bool disposedSecond = false;
+    __block int result = 0;
+    
+    SSignal *signal = [[SSignal alloc] initWithGenerator:^id<SDisposable>(SSubscriber *subscriber)
+    {
+        generatedFirst = true;
+        [subscriber putNext:@(1)];
+        [subscriber putCompletion];
+        return [[SBlockDisposable alloc] initWithBlock:^
+        {
+            disposedFirst = true;
+        }];
+    }];
+    
+    signal = [signal then:[[SSignal alloc] initWithGenerator:^id<SDisposable>(SSubscriber *subscriber)
+    {
+        generatedSecond = true;
+        [subscriber putNext:@(2)];
+        [subscriber putCompletion];
+        return [[SBlockDisposable alloc] initWithBlock:^
+        {
+            disposedSecond = true;
+        }];
+    }]];
+    
+    [signal startWithNext:^(id next)
+    {
+        result += [next intValue];
+    }];
+    
+    XCTAssertTrue(generatedFirst);
+    XCTAssertTrue(disposedFirst);
+    XCTAssertTrue(generatedSecond);
+    XCTAssertTrue(disposedSecond);
+    XCTAssert(result == 3);
+}
+
+- (void)testSwitchToLatest
+{
+    __block int result = 0;
+    __block bool disposedOne = false;
+    __block bool disposedTwo = false;
+    __block bool disposedThree = false;
+    __block bool completedAll = false;
+    
+    bool deallocatedOne = false;
+    bool deallocatedTwo = false;
+    bool deallocatedThree = false;
+    
+    @autoreleasepool
+    {
+        DeallocatingObject *objectOne = [[DeallocatingObject alloc] initWithDeallocated:&deallocatedOne];
+        DeallocatingObject *objectTwo = [[DeallocatingObject alloc] initWithDeallocated:&deallocatedTwo];
+        DeallocatingObject *objectThree = [[DeallocatingObject alloc] initWithDeallocated:&deallocatedThree];
+
+        SSignal *one = [[SSignal alloc] initWithGenerator:^id<SDisposable>(SSubscriber *subscriber)
+        {
+            [subscriber putNext:@(1)];
+            [subscriber putCompletion];
+            __unused id a0 = [objectOne description];
+            return [[SBlockDisposable alloc] initWithBlock:^
+            {
+                __unused id a0 = [objectOne description];
+                disposedOne = true;
+            }];
+        }];
+        SSignal *two = [[SSignal alloc] initWithGenerator:^id<SDisposable>(SSubscriber *subscriber)
+        {
+            [subscriber putNext:@(2)];
+            [subscriber putCompletion];
+            __unused id a1 = [objectTwo description];
+            return [[SBlockDisposable alloc] initWithBlock:^
+            {
+                __unused id a1 = [objectOne description];
+                disposedTwo = true;
+            }];
+        }];
+        SSignal *three = [[SSignal alloc] initWithGenerator:^id<SDisposable>(SSubscriber *subscriber)
+        {
+            [subscriber putNext:@(3)];
+            [subscriber putCompletion];
+            __unused id a0 = [objectThree description];
+            return [[SBlockDisposable alloc] initWithBlock:^
+            {
+                __unused id a1 = [objectOne description];
+                disposedThree = true;
+            }];
+        }];
+        
+        SSignal *signal = [[[[SSignal single:one] then:[SSignal single:two]] then:[SSignal single:three]] switchToLatest];
+        [signal startWithNext:^(id next)
+        {
+            result += [next intValue];
+        } error:nil completed:^
+        {
+            completedAll = true;
+        }];
+    }
+    
+    XCTAssert(result == 6);
+    XCTAssertTrue(disposedOne);
+    XCTAssertTrue(disposedTwo);
+    XCTAssertTrue(disposedThree);
+    XCTAssertTrue(deallocatedOne);
+    XCTAssertTrue(deallocatedTwo);
+    XCTAssertTrue(deallocatedThree);
+    XCTAssertTrue(completedAll);
+}
+
+- (void)testSwitchToLatestError
+{
+    __block bool errorGenerated = false;
+    
+    SSignal *one = [[SSignal alloc] initWithGenerator:^id<SDisposable>(SSubscriber *subscriber)
+    {
+        [subscriber putError:nil];
+        return nil;
+    }];
+    
+    [one startWithNext:^(__unused id next)
+    {
+        
+    } error:^(__unused id error)
+    {
+        errorGenerated = true;
+    } completed:^
+    {
+        
+    }];
+    
+    XCTAssertTrue(errorGenerated);
+}
+
+- (void)testSwitchToLatestCompleted
+{
+    __block bool completedAll = false;
+    
+    SSignal *one = [[SSignal alloc] initWithGenerator:^id<SDisposable>(SSubscriber *subscriber)
+    {
+        [subscriber putCompletion];
+        return nil;
+    }];
+    
+    [one startWithNext:^(__unused id next)
+    {
+        
+    } error:^(__unused id error)
+    {
+    } completed:^
+    {
+        completedAll = true;
+    }];
+    
+    XCTAssertTrue(completedAll);
+}
+
 @end