diff --git a/SDWebImage/Core/SDWebImageManager.m b/SDWebImage/Core/SDWebImageManager.m
index 3b29632d..d5be68f6 100644
--- a/SDWebImage/Core/SDWebImageManager.m
+++ b/SDWebImage/Core/SDWebImageManager.m
@@ -17,7 +17,9 @@
 static id<SDImageCache> _defaultImageCache;
 static id<SDImageLoader> _defaultImageLoader;
 
-@interface SDWebImageCombinedOperation ()
+@interface SDWebImageCombinedOperation () {
+    SD_LOCK_DECLARE(_cancelledLock); // a lock to keep the access to `cancelled` thread-safe
+}
 
 @property (assign, nonatomic, getter = isCancelled) BOOL cancelled;
 @property (strong, nonatomic, readwrite, nullable) id<SDWebImageOperation> loaderOperation;
@@ -803,22 +805,38 @@ static id<SDImageLoader> _defaultImageLoader;
 
 @implementation SDWebImageCombinedOperation
 
-- (void)cancel {
-    @synchronized(self) {
-        if (self.isCancelled) {
-            return;
-        }
-        self.cancelled = YES;
-        if (self.cacheOperation) {
-            [self.cacheOperation cancel];
-            self.cacheOperation = nil;
-        }
-        if (self.loaderOperation) {
-            [self.loaderOperation cancel];
-            self.loaderOperation = nil;
-        }
-        [self.manager safelyRemoveOperationFromRunning:self];
+- (instancetype)init {
+    if (self = [super init]) {
+        SD_LOCK_INIT(_cancelledLock);
     }
+
+    return self;
+}
+
+- (BOOL)isCancelled {
+    BOOL isCancelled = NO;
+    SD_LOCK(_cancelledLock);
+    isCancelled = _cancelled;
+    SD_UNLOCK(_cancelledLock);
+    return isCancelled;
+}
+
+- (void)cancel {
+    SD_LOCK(_cancelledLock);
+    if (_cancelled) {
+        return;
+    }
+    _cancelled = YES;
+    if (self.cacheOperation) {
+        [self.cacheOperation cancel];
+        self.cacheOperation = nil;
+    }
+    if (self.loaderOperation) {
+        [self.loaderOperation cancel];
+        self.loaderOperation = nil;
+    }
+    [self.manager safelyRemoveOperationFromRunning:self];
+    SD_UNLOCK(_cancelledLock);
 }
 
 @end