diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8a2ff436..4ba6a3e7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Parsing of AVCDecoderConfigurationRecord
 - Parsing of time offset in AVC PicTiming SEI
+- Set senc.perSampleIVSize properly
 
 ## [0.40.2] - 2023-11-17
 
diff --git a/mp4/senc.go b/mp4/senc.go
index c038cd00..0a66527c 100644
--- a/mp4/senc.go
+++ b/mp4/senc.go
@@ -146,6 +146,7 @@ func (s *SencBox) ParseReadBox(perSampleIVSize byte, saiz *SaizBox) error {
 		// No subsamples
 		if perSampleIVSize == 0 { // Infer the size
 			perSampleIVSize = byte(nrBytesLeft / s.SampleCount)
+			s.perSampleIVSize = perSampleIVSize
 		}
 
 		s.IVs = make([]InitializationVector, 0, s.SampleCount)
diff --git a/mp4/senc_test.go b/mp4/senc_test.go
index 1ed21d08..be227b26 100644
--- a/mp4/senc_test.go
+++ b/mp4/senc_test.go
@@ -124,3 +124,26 @@ func TestAddSamples(t *testing.T) {
 	err = senc.AddSample(SencSample{iv8, []SubSamplePattern{{20, 2000}}})
 	assertError(t, err, "Should have got error due to different iv size")
 }
+
+// TestImplicitIVSize tests that the implicit IV size is correctly calculated (perSampleIVSize != 0)
+func TestImplicitIVSize(t *testing.T) {
+	testCases := []struct {
+		inputFile        string
+		expectedSencSize int
+	}{
+		{inputFile: "testdata/2xSencNoMdat.mp4", expectedSencSize: 2248},
+	}
+
+	for _, tc := range testCases {
+		// Read the file
+		m, err := ReadMP4File(tc.inputFile)
+		if err != nil {
+			t.Error(err)
+		}
+		frag := m.Segments[0].Fragments[0]
+		senc := frag.Moof.Traf.Senc
+		if int(senc.Size()) != tc.expectedSencSize {
+			t.Errorf("Expected senc size %d, got %d", tc.expectedSencSize, senc.Size())
+		}
+	}
+}
diff --git a/mp4/testdata/2xSencNoMdat.mp4 b/mp4/testdata/2xSencNoMdat.mp4
new file mode 100644
index 00000000..d82ca7d6
Binary files /dev/null and b/mp4/testdata/2xSencNoMdat.mp4 differ