diff --git a/FBSimulatorControlTests/Tests/Integration/FBSimulatorPoolTests.m b/FBSimulatorControlTests/Tests/Integration/FBSimulatorPoolTests.m
index 19fc1e1a..9a0e2e72 100644
--- a/FBSimulatorControlTests/Tests/Integration/FBSimulatorPoolTests.m
+++ b/FBSimulatorControlTests/Tests/Integration/FBSimulatorPoolTests.m
@@ -35,8 +35,8 @@
   ]];
 
   [self mockAllocationOfSimulatorsUDIDs:@[
-    [mockedSimulators[0] UDID],
-    [mockedSimulators[3] UDID]
+    [mockedSimulators[0] udid],
+    [mockedSimulators[3] udid]
   ]];
 
   NSArray *simulators = self.pool.allocatedSimulators;
diff --git a/FBSimulatorControlTests/Utilities/FBSimulatorPoolTestCase.h b/FBSimulatorControlTests/Utilities/FBSimulatorPoolTestCase.h
index 7cc655ed..f9629c7f 100644
--- a/FBSimulatorControlTests/Utilities/FBSimulatorPoolTestCase.h
+++ b/FBSimulatorControlTests/Utilities/FBSimulatorPoolTestCase.h
@@ -37,6 +37,6 @@
 /**
  Mocks the Allocation of Simulators based on their UDID.
  */
-- (void)mockAllocationOfSimulatorsUDIDs:(NSArray *)deviceUDIDs;
+- (void)mockAllocationOfSimulatorsUDIDs:(NSArray<NSString *> *)deviceUDIDs;
 
 @end
diff --git a/FBSimulatorControlTests/Utilities/FBSimulatorPoolTestCase.m b/FBSimulatorControlTests/Utilities/FBSimulatorPoolTestCase.m
index c5e1ab81..930db21f 100644
--- a/FBSimulatorControlTests/Utilities/FBSimulatorPoolTestCase.m
+++ b/FBSimulatorControlTests/Utilities/FBSimulatorPoolTestCase.m
@@ -65,12 +65,12 @@
   return simulators;
 }
 
-- (void)mockAllocationOfSimulatorsUDIDs:(NSArray *)deviceUDIDs
+- (void)mockAllocationOfSimulatorsUDIDs:(NSArray<NSString *> *)deviceUDIDs
 {
-  NSDictionary *simulatorsByUDID = [NSDictionary dictionaryWithObjects:self.set.allSimulators forKeys:[self.set.allSimulators valueForKey:@"udid"]];
-  for (NSUUID *udid in deviceUDIDs) {
-    [self.pool.allocatedUDIDs addObject:udid.UUIDString];
-    [simulatorsByUDID[udid.UUIDString] setPool:self.pool];
+  NSDictionary<NSString *, FBSimulator *> *simulatorsByUDID = [NSDictionary dictionaryWithObjects:self.set.allSimulators forKeys:[self.set.allSimulators valueForKey:@"udid"]];
+  for (NSString *udid in deviceUDIDs) {
+    [self.pool.allocatedUDIDs addObject:udid];
+    [simulatorsByUDID[udid] setPool:self.pool];
   }
 }