diff --git a/SDWebImage/Core/SDImageIOAnimatedCoder.m b/SDWebImage/Core/SDImageIOAnimatedCoder.m
index b1bd1b24..e5247cb1 100644
--- a/SDWebImage/Core/SDImageIOAnimatedCoder.m
+++ b/SDWebImage/Core/SDImageIOAnimatedCoder.m
@@ -499,7 +499,9 @@ static NSString * kSDCGImageDestinationRequestedFileSize = @"kCGImageDestination
     CGFloat pixelWidth = (CGFloat)CGImageGetWidth(imageRef);
     CGFloat pixelHeight = (CGFloat)CGImageGetHeight(imageRef);
     CGFloat finalPixelSize = 0;
-    if (maxPixelSize.width > 0 && maxPixelSize.height > 0 && pixelWidth > maxPixelSize.width && pixelHeight > maxPixelSize.height) {
+    BOOL encodeFullImage = maxPixelSize.width == 0 || maxPixelSize.height == 0 || pixelWidth == 0 || pixelHeight == 0 || (pixelWidth <= maxPixelSize.width && pixelHeight <= maxPixelSize.height);
+    if (!encodeFullImage) {
+        // Thumbnail Encoding
         CGFloat pixelRatio = pixelWidth / pixelHeight;
         CGFloat maxPixelSizeRatio = maxPixelSize.width / maxPixelSize.height;
         if (pixelRatio > maxPixelSizeRatio) {
diff --git a/SDWebImage/Core/SDImageIOCoder.m b/SDWebImage/Core/SDImageIOCoder.m
index 7149b444..7b5b4a8a 100644
--- a/SDWebImage/Core/SDImageIOCoder.m
+++ b/SDWebImage/Core/SDImageIOCoder.m
@@ -252,10 +252,12 @@ static NSString * kSDCGImageDestinationRequestedFileSize = @"kCGImageDestination
     }
     CGFloat pixelWidth = (CGFloat)CGImageGetWidth(imageRef);
     CGFloat pixelHeight = (CGFloat)CGImageGetHeight(imageRef);
-    if (maxPixelSize.width > 0 && maxPixelSize.height > 0 && pixelWidth > maxPixelSize.width && pixelHeight > maxPixelSize.height) {
+    CGFloat finalPixelSize = 0;
+    BOOL encodeFullImage = maxPixelSize.width == 0 || maxPixelSize.height == 0 || pixelWidth == 0 || pixelHeight == 0 || (pixelWidth <= maxPixelSize.width && pixelHeight <= maxPixelSize.height);
+    if (!encodeFullImage) {
+        // Thumbnail Encoding
         CGFloat pixelRatio = pixelWidth / pixelHeight;
         CGFloat maxPixelSizeRatio = maxPixelSize.width / maxPixelSize.height;
-        CGFloat finalPixelSize;
         if (pixelRatio > maxPixelSizeRatio) {
             finalPixelSize = MAX(maxPixelSize.width, maxPixelSize.width / pixelRatio);
         } else {
diff --git a/Tests/Tests/SDImageCoderTests.m b/Tests/Tests/SDImageCoderTests.m
index ba927abc..b8e09da7 100644
--- a/Tests/Tests/SDImageCoderTests.m
+++ b/Tests/Tests/SDImageCoderTests.m
@@ -341,7 +341,7 @@
     }
 }
 
-- (void)test22ThatThumbnailPreserveAspectRatio {
+- (void)test22ThatThumbnailDecodeCalculation {
     NSString *testImagePath = [[NSBundle bundleForClass:[self class]] pathForResource:@"TestImageLarge" ofType:@"jpg"];
     NSData *testImageData = [NSData dataWithContentsOfFile:testImagePath];
     CGSize thumbnailSize = CGSizeMake(400, 300);
@@ -353,6 +353,19 @@
     expect(imageSize.height).equal(263);
 }
 
+- (void)test23ThatThumbnailEncodeCalculation {
+    NSString *testImagePath = [[NSBundle bundleForClass:[self class]] pathForResource:@"TestImageLarge" ofType:@"jpg"];
+    NSData *testImageData = [NSData dataWithContentsOfFile:testImagePath];
+    UIImage *image = [SDImageIOCoder.sharedCoder decodedImageWithData:testImageData options:nil];
+    expect(image.size).equal(CGSizeMake(5250, 3450));
+    CGSize thumbnailSize = CGSizeMake(4000, 4000); // 3450 < 4000 < 5250
+    NSData *encodedData = [SDImageIOCoder.sharedCoder encodedDataWithImage:image format:SDImageFormatJPEG options:@{
+            SDImageCoderEncodeMaxPixelSize: @(thumbnailSize)
+    }];
+    UIImage *encodedImage = [UIImage sd_imageWithData:encodedData];
+    expect(encodedImage.size).equal(CGSizeMake(4000, 2629));
+}
+
 #pragma mark - Utils
 
 - (void)verifyCoder:(id<SDImageCoder>)coder