diff --git a/format/mpeg/mpeg_spu.go b/format/mpeg/mpeg_spu.go
index deacaafc..a645e7a8 100644
--- a/format/mpeg/mpeg_spu.go
+++ b/format/mpeg/mpeg_spu.go
@@ -103,6 +103,9 @@ func spuDecode(d *decode.D, in interface{}) interface{} {
 	d.FieldU16("size")
 	dcsqtOffset := d.FieldU16("dcsqt_offset")
 
+	// to catch infinite loops
+	offsetSeen := map[uint64]struct{}{}
+
 	d.SeekAbs(int64(dcsqtOffset) * 8)
 	d.FieldArray("dcsqt", func(d *decode.D) {
 		lastDCSQ := false
@@ -117,6 +120,11 @@ func spuDecode(d *decode.D, in interface{}) interface{} {
 					return
 				}
 
+				if _, ok := offsetSeen[offset]; ok {
+					d.Fatalf("dcsqt loop detected for %d", offset)
+				}
+				offsetSeen[offset] = struct{}{}
+
 				var pxdTFOffset int64
 				var pxdBFOffset int64
 				var width uint64