diff --git a/macosx/PortChecker.h b/macosx/PortChecker.h
index 8dd41aa11..32e20227d 100644
--- a/macosx/PortChecker.h
+++ b/macosx/PortChecker.h
@@ -4,6 +4,8 @@
 
 #import <Foundation/Foundation.h>
 
+NS_ASSUME_NONNULL_BEGIN
+
 typedef NS_ENUM(unsigned int, port_status_t) { //
     PORT_STATUS_CHECKING,
     PORT_STATUS_OPEN,
@@ -27,3 +29,5 @@ typedef NS_ENUM(unsigned int, port_status_t) { //
 - (void)portCheckerDidFinishProbing:(PortChecker*)portChecker;
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/macosx/PortChecker.mm b/macosx/PortChecker.mm
index a50836ee9..dd068b07b 100644
--- a/macosx/PortChecker.mm
+++ b/macosx/PortChecker.mm
@@ -11,8 +11,8 @@ static NSTimeInterval const kCheckFireInterval = 3.0;
 @property(nonatomic, weak) NSObject<PortCheckerDelegate>* fDelegate;
 @property(nonatomic) port_status_t fStatus;
 
-@property(nonatomic) NSURLConnection* fConnection;
-@property(nonatomic) NSMutableData* fPortProbeData;
+@property(nonatomic) NSURLSession* fSession;
+@property(nonatomic) NSURLSessionDataTask* fTask;
 
 @property(nonatomic) NSTimer* fTimer;
 
@@ -24,6 +24,8 @@ static NSTimeInterval const kCheckFireInterval = 3.0;
 {
     if ((self = [super init]))
     {
+        _fSession = [NSURLSession sessionWithConfiguration:NSURLSessionConfiguration.ephemeralSessionConfiguration delegate:nil
+                                             delegateQueue:nil];
         _fDelegate = delegate;
 
         _fStatus = PORT_STATUS_CHECKING;
@@ -42,7 +44,7 @@ static NSTimeInterval const kCheckFireInterval = 3.0;
 
 - (void)dealloc
 {
-    [_fTimer invalidate];
+    [self cancelProbe];
 }
 
 - (port_status_t)status
@@ -55,51 +57,7 @@ static NSTimeInterval const kCheckFireInterval = 3.0;
     [self.fTimer invalidate];
     self.fTimer = nil;
 
-    [self.fConnection cancel];
-}
-
-- (void)connection:(NSURLConnection*)connection didReceiveResponse:(NSURLResponse*)response
-{
-    self.fPortProbeData.length = 0;
-}
-
-- (void)connection:(NSURLConnection*)connection didReceiveData:(NSData*)data
-{
-    [self.fPortProbeData appendData:data];
-}
-
-- (void)connection:(NSURLConnection*)connection didFailWithError:(NSError*)error
-{
-    NSLog(@"Unable to get port status: connection failed (%@)", error.localizedDescription);
-    [self callBackWithStatus:PORT_STATUS_ERROR];
-}
-
-- (void)connectionDidFinishLoading:(NSURLConnection*)connection
-{
-    NSString* probeString = [[NSString alloc] initWithData:self.fPortProbeData encoding:NSUTF8StringEncoding];
-    self.fPortProbeData = nil;
-
-    if (probeString)
-    {
-        if ([probeString isEqualToString:@"1"])
-        {
-            [self callBackWithStatus:PORT_STATUS_OPEN];
-        }
-        else if ([probeString isEqualToString:@"0"])
-        {
-            [self callBackWithStatus:PORT_STATUS_CLOSED];
-        }
-        else
-        {
-            NSLog(@"Unable to get port status: invalid response (%@)", probeString);
-            [self callBackWithStatus:PORT_STATUS_ERROR];
-        }
-    }
-    else
-    {
-        NSLog(@"Unable to get port status: invalid data received");
-        [self callBackWithStatus:PORT_STATUS_ERROR];
-    }
+    [self.fTask cancel];
 }
 
 #pragma mark - Private
@@ -108,30 +66,48 @@ static NSTimeInterval const kCheckFireInterval = 3.0;
 {
     self.fTimer = nil;
 
-    NSString* urlString = [NSString stringWithFormat:@"https://portcheck.transmissionbt.com/%ld", [timer.userInfo integerValue]];
+    NSString* urlString = [NSString stringWithFormat:@"https://portcheck.transmissionbt.com/%ld", [(NSNumber*)timer.userInfo integerValue]];
     NSURLRequest* portProbeRequest = [NSURLRequest requestWithURL:[NSURL URLWithString:urlString]
                                                       cachePolicy:NSURLRequestReloadIgnoringLocalAndRemoteCacheData
                                                   timeoutInterval:15.0];
 
-    if ((self.fConnection = [[NSURLConnection alloc] initWithRequest:portProbeRequest delegate:self]))
-    {
-        self.fPortProbeData = [[NSMutableData alloc] init];
-    }
-    else
-    {
-        NSLog(@"Unable to get port status: failed to initiate connection");
-        [self callBackWithStatus:PORT_STATUS_ERROR];
-    }
+    _fTask = [_fSession dataTaskWithRequest:portProbeRequest
+                          completionHandler:^(NSData* _Nullable data, NSURLResponse* _Nullable response, NSError* _Nullable error) {
+                              if (error)
+                              {
+                                  NSLog(@"Unable to get port status: connection failed (%@)", error.localizedDescription);
+                                  [self callBackWithStatus:PORT_STATUS_ERROR];
+                                  return;
+                              }
+                              NSString* probeString = [[NSString alloc] initWithData:data ?: NSData.data encoding:NSUTF8StringEncoding];
+                              if (!probeString)
+                              {
+                                  NSLog(@"Unable to get port status: invalid data received");
+                                  [self callBackWithStatus:PORT_STATUS_ERROR];
+                              }
+                              else if ([probeString isEqualToString:@"1"])
+                              {
+                                  [self callBackWithStatus:PORT_STATUS_OPEN];
+                              }
+                              else if ([probeString isEqualToString:@"0"])
+                              {
+                                  [self callBackWithStatus:PORT_STATUS_CLOSED];
+                              }
+                              else
+                              {
+                                  NSLog(@"Unable to get port status: invalid response (%@)", probeString);
+                                  [self callBackWithStatus:PORT_STATUS_ERROR];
+                              }
+                          }];
+    [_fTask resume];
 }
 
 - (void)callBackWithStatus:(port_status_t)status
 {
     self.fStatus = status;
 
-    if (self.fDelegate && [self.fDelegate respondsToSelector:@selector(portCheckerDidFinishProbing:)])
-    {
-        [self.fDelegate performSelectorOnMainThread:@selector(portCheckerDidFinishProbing:) withObject:self waitUntilDone:NO];
-    }
+    NSObject<PortCheckerDelegate>* delegate = self.fDelegate;
+    [delegate performSelectorOnMainThread:@selector(portCheckerDidFinishProbing:) withObject:self waitUntilDone:NO];
 }
 
 @end
diff --git a/macosx/PrefsController.mm b/macosx/PrefsController.mm
index cb62b82eb..a66c6eab9 100644
--- a/macosx/PrefsController.mm
+++ b/macosx/PrefsController.mm
@@ -495,7 +495,7 @@ static NSString* const kWebUIURLFormat = @"http://localhost:%ld/";
     case PORT_STATUS_CHECKING:
         break;
     default:
-        NSAssert1(NO, @"Port checker returned invalid status: %d", self.fPortChecker.status);
+        NSAssert(NO, @"Port checker returned invalid status: %d", self.fPortChecker.status);
         break;
     }
     self.fPortChecker = nil;