diff --git a/RxSwift/RxSwift/Observables/Observable+Creation.swift b/RxSwift/RxSwift/Observables/Observable+Creation.swift
index c27ac0f8..c4b89166 100644
--- a/RxSwift/RxSwift/Observables/Observable+Creation.swift
+++ b/RxSwift/RxSwift/Observables/Observable+Creation.swift
@@ -63,7 +63,7 @@ public func from<E, S where S: SequenceType, S.Generator.Element == E>(sequence:
         }
         
         sendCompleted(observer)
-        return DefaultDisposable()
+        return NopDisposable.instance
     }
 }
 
diff --git a/RxTests/RxSwiftTests/Tests/Observable+ConcurrencyTest.swift b/RxTests/RxSwiftTests/Tests/Observable+ConcurrencyTest.swift
index d1680052..94915e53 100644
--- a/RxTests/RxSwiftTests/Tests/Observable+ConcurrencyTest.swift
+++ b/RxTests/RxSwiftTests/Tests/Observable+ConcurrencyTest.swift
@@ -491,7 +491,7 @@ extension ObservableConcurrencyTest {
     }
     
     func testObserveOn_EnsureTestsAreExecutedWithRealConcurrentScheduler() {
-        var variable: Int32 = 0
+        var variable: Int = 0
         
         var events: [String] = []
         
@@ -503,6 +503,8 @@ extension ObservableConcurrencyTest {
                 }
                 
                 while variable != 2 {
+                    // to kill compiler optimizations
+                    self.performLocked { }
                     if variable == 0 {
                         variable = 1
                     }
@@ -516,11 +518,14 @@ extension ObservableConcurrencyTest {
             }
             
             let disposable2 = scheduler.schedule(()) { _ in
+                    //println("variable \(variable)")
                 self.performLocked {
                     events.append("Started")
                 }
                 
                 while variable != 2 {
+                    // to kill compiler optimizations
+                    self.performLocked { }
                     if variable == 1 {
                         variable = 2
                     }
diff --git a/RxTests/RxTests.xcodeproj/project.pbxproj b/RxTests/RxTests.xcodeproj/project.pbxproj
index 71447215..9fc2f75e 100644
--- a/RxTests/RxTests.xcodeproj/project.pbxproj
+++ b/RxTests/RxTests.xcodeproj/project.pbxproj
@@ -84,6 +84,7 @@
 		C8E381291B207D03008CDC33 /* PrimitiveHotObservable.swift in Sources */ = {isa = PBXBuildFile; fileRef = C8E381271B207D03008CDC33 /* PrimitiveHotObservable.swift */; };
 		C8E3812B1B2083C2008CDC33 /* PrimitiveMockObserver.swift in Sources */ = {isa = PBXBuildFile; fileRef = C8E3812A1B2083C2008CDC33 /* PrimitiveMockObserver.swift */; };
 		C8E3812C1B2083C2008CDC33 /* PrimitiveMockObserver.swift in Sources */ = {isa = PBXBuildFile; fileRef = C8E3812A1B2083C2008CDC33 /* PrimitiveMockObserver.swift */; };
+		C8E3813A1B21B77E008CDC33 /* Observable+Extensions.swift in Sources */ = {isa = PBXBuildFile; fileRef = C8E381221B2063CC008CDC33 /* Observable+Extensions.swift */; };
 /* End PBXBuildFile section */
 
 /* Begin PBXFileReference section */
@@ -444,6 +445,7 @@
 				C88BB8AB1B07E64B0064D411 /* TestExtensions.swift in Sources */,
 				C88BB8AC1B07E64B0064D411 /* AssumptionsTest.swift in Sources */,
 				C88BB8AD1B07E64B0064D411 /* ConnectableObservable.swift in Sources */,
+				C8E3813A1B21B77E008CDC33 /* Observable+Extensions.swift in Sources */,
 				C88BB8AE1B07E64B0064D411 /* VariableTest.swift in Sources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;