diff --git a/src/ImageSharp/Formats/Jpeg/JpegDecoderCore.cs b/src/ImageSharp/Formats/Jpeg/JpegDecoderCore.cs
index 02ae022e11..06c844d58e 100644
--- a/src/ImageSharp/Formats/Jpeg/JpegDecoderCore.cs
+++ b/src/ImageSharp/Formats/Jpeg/JpegDecoderCore.cs
@@ -859,6 +859,11 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
         /// </summary>
         private void ProcessStartOfScanMarker()
         {
+            if (this.Frame is null)
+            {
+                throw new ImageFormatException("No readable SOFn (Start Of Frame) marker found.");
+            }
+
             int selectorsCount = this.InputStream.ReadByte();
             for (int i = 0; i < selectorsCount; i++)
             {
diff --git a/tests/ImageSharp.Tests/Formats/Jpg/JpegDecoderTests.Baseline.cs b/tests/ImageSharp.Tests/Formats/Jpg/JpegDecoderTests.Baseline.cs
index 73167a4b7e..a2f57e485a 100644
--- a/tests/ImageSharp.Tests/Formats/Jpg/JpegDecoderTests.Baseline.cs
+++ b/tests/ImageSharp.Tests/Formats/Jpg/JpegDecoderTests.Baseline.cs
@@ -42,5 +42,13 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg
             // TODO: We need a public ImageDecoderException class in ImageSharp!
             Assert.ThrowsAny<Exception>(() => provider.GetImage(JpegDecoder));
         }
+
+        [Theory]
+        [WithFile(TestImages.Jpeg.Issues.InvalidJpegThrowsWrongException797, PixelTypes.Rgba32)]
+        public void LoadingImage_InvalidTagLength_ShouldThrow<TPixel>(TestImageProvider<TPixel> provider)
+            where TPixel : struct, IPixel<TPixel>
+        {
+            Assert.Throws<ImageFormatException>(() => provider.GetImage());
+        }
     }
 }
\ No newline at end of file
diff --git a/tests/ImageSharp.Tests/TestImages.cs b/tests/ImageSharp.Tests/TestImages.cs
index 6141e9e2a0..460aceba0a 100644
--- a/tests/ImageSharp.Tests/TestImages.cs
+++ b/tests/ImageSharp.Tests/TestImages.cs
@@ -167,6 +167,7 @@ namespace SixLabors.ImageSharp.Tests
                 public const string OrderedInterleavedProgressive723C = "Jpg/issues/Issue723-Ordered-Interleaved-Progressive-C.jpg";
                 public const string ExifGetString750Transform = "Jpg/issues/issue750-exif-tranform.jpg";
                 public const string ExifGetString750Load = "Jpg/issues/issue750-exif-load.jpg";
+                public const string InvalidJpegThrowsWrongException797 = "Jpg/issues/Issue797-InvalidImage.jpg";
             }
 
             public static readonly string[] All = Baseline.All.Concat(Progressive.All).ToArray();
diff --git a/tests/Images/Input/Jpg/issues/Issue797-InvalidImage.jpg b/tests/Images/Input/Jpg/issues/Issue797-InvalidImage.jpg
new file mode 100644
index 0000000000..7c9190fbdb
--- /dev/null
+++ b/tests/Images/Input/Jpg/issues/Issue797-InvalidImage.jpg
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:2c3c6a09c1ed868bb18c7c5038da743a88dbfd10762a2b12260053adf63b376f
+size 381