diff --git a/pkg/obiapat/pattern.go b/pkg/obiapat/pattern.go
index 714c978..25a3c7b 100755
--- a/pkg/obiapat/pattern.go
+++ b/pkg/obiapat/pattern.go
@@ -374,6 +374,17 @@ func (pattern ApatPattern) BestMatch(sequence ApatSequence, begin, length int) (
 	cpattern := (*[1 << 30]byte)(unsafe.Pointer(pattern.pointer.pointer.cpat))
 	frg := sequence.pointer.reference.Sequence()[start:end]
 
+	if len(frg) <= int(pattern.pointer.pointer.patlen) {
+		// The sequence is too short (e.g. the match is near one of its
+		// ends) to extract a fragment longer than the pattern, which
+		// obialign.LocatePattern requires. Keep the original match
+		// instead of refining it.
+		start = best[0]
+		end = best[1]
+		log.Debugln("Fragment too short for indel relocation, keeping original match", start, end, nerr)
+		return
+	}
+
 	log.Debugln(
 		string(frg),
 		string((*cpattern)[0:int(pattern.pointer.pointer.patlen)]),
@@ -480,18 +491,25 @@ func (pattern ApatPattern) AllMatches(sequence ApatSequence, begin, length int)
 			cpattern := (*[1 << 30]byte)(unsafe.Pointer(pattern.pointer.pointer.cpat))
 			frg := sequence.pointer.reference.Sequence()[start:end]
 
-			pb, pe, score := obialign.LocatePattern(
-				sequence.pointer.reference.Id(),
-				(*cpattern)[0:int(pattern.pointer.pointer.patlen)],
-				frg)
+			// obialign.LocatePattern requires the fragment to be strictly
+			// longer than the pattern. When the match sits near one of the
+			// sequence ends, the fragment can be clamped to the sequence
+			// boundaries and end up too short; in that case keep the
+			// original (unrefined) match instead of crashing.
+			if len(frg) > int(pattern.pointer.pointer.patlen) {
+				pb, pe, score := obialign.LocatePattern(
+					sequence.pointer.reference.Id(),
+					(*cpattern)[0:int(pattern.pointer.pointer.patlen)],
+					frg)
 
-			// olderr := m[2]
-			m[2] = score
-			m[0] = start + pb
-			m[1] = start + pe
+				// olderr := m[2]
+				m[2] = score
+				m[0] = start + pb
+				m[1] = start + pe
 
-			// obilog.Warnf("seq[%d@%d:%d] %d: %s %d - %s:%s:%s", i, m[0], m[1], olderr, sequence.pointer.reference.Id(), score,
-			// 	frg, (*cpattern)[0:int(pattern.pointer.pointer.patlen)], sequence.pointer.reference.Sequence()[m[0]:m[1]])
+				// obilog.Warnf("seq[%d@%d:%d] %d: %s %d - %s:%s:%s", i, m[0], m[1], olderr, sequence.pointer.reference.Id(), score,
+				// 	frg, (*cpattern)[0:int(pattern.pointer.pointer.patlen)], sequence.pointer.reference.Sequence()[m[0]:m[1]])
+			}
 		}
 
 		if int(pattern.pointer.pointer.maxerr) >= m[2] {
diff --git a/pkg/obiformats/fastqseq_read.go b/pkg/obiformats/fastqseq_read.go
index 861705f..125c838 100644
--- a/pkg/obiformats/fastqseq_read.go
+++ b/pkg/obiformats/fastqseq_read.go
@@ -131,7 +131,7 @@ func _storeSequenceQuality(bytes *bytes.Buffer, out *obiseq.BioSequence, quality
 	out.SetQualities(q)
 }
 
-func FastqChunkParser(quality_shift byte, with_quality bool, UtoT bool) func(string, io.Reader) (obiseq.BioSequenceSlice, error) {
+func FastqChunkParser(quality_shift byte, with_quality bool, UtoT bool, fileName string) func(string, io.Reader) (obiseq.BioSequenceSlice, error) {
 	parser := func(source string, input io.Reader) (obiseq.BioSequenceSlice, error) {
 
 		var identifier string
@@ -160,12 +160,12 @@ func FastqChunkParser(quality_shift byte, with_quality bool, UtoT bool) func(str
 					// Beginning of sequence
 					state = 1
 				} else {
-					log.Fatalf("%s : sequence entry is not starting with @", source)
+					log.Fatalf("file %s: sequence entry is not starting with @", fileName)
 				}
 			case 1: // Beginning of identifier (Mandatory)
 				if is_sep {
 					// No identifier -> ERROR
-					log.Fatalf("%s : sequence identifier is empty", source)
+					log.Fatalf("file %s: sequence identifier is empty", fileName)
 				} else {
 					// Beginning of identifier
 					state = 2
@@ -221,7 +221,7 @@ func FastqChunkParser(quality_shift byte, with_quality bool, UtoT bool) func(str
 					// End of sequence
 					rawseq := seqBytes.Bytes()
 					if len(rawseq) == 0 {
-						log.Fatalf("@%s[%s] : sequence is empty", identifier, source)
+						log.Fatalf("file %s: record @%s has an empty sequence line", fileName, identifier)
 					}
 					s := obiseq.NewBioSequence(identifier, rawseq, definition)
 					s.SetSource(source)
@@ -241,8 +241,8 @@ func FastqChunkParser(quality_shift byte, with_quality bool, UtoT bool) func(str
 						context = append(
 							append([]byte{previous}, C),
 							context...)
-						log.Fatalf("%s [%s]: sequence contains invalid character %c (%s)",
-							source, identifier, C, string(context))
+						log.Fatalf("file %s: record @%s contains invalid character %c (%s)",
+							fileName, identifier, C, string(context))
 					}
 				}
 			case 7:
@@ -251,7 +251,7 @@ func FastqChunkParser(quality_shift byte, with_quality bool, UtoT bool) func(str
 				} else if C == '+' {
 					state = 8
 				} else {
-					log.Fatalf("@%s[%s] : sequence data not followed by a line starting with + but a %c", identifier, source, C)
+					log.Fatalf("file %s: record @%s: sequence data not followed by a line starting with + but a %c", fileName, identifier, C)
 				}
 			case 8:
 				// State consuming the + internal header line
@@ -282,7 +282,7 @@ func FastqChunkParser(quality_shift byte, with_quality bool, UtoT bool) func(str
 				} else if C == '@' {
 					state = 1
 				} else {
-					log.Fatalf("%s[%s] : sequence record not followed by a line starting with @", identifier, source)
+					log.Fatalf("file %s: record @%s not followed by a line starting with @", fileName, identifier)
 				}
 
 			}
@@ -304,7 +304,7 @@ func FastqChunkParser(quality_shift byte, with_quality bool, UtoT bool) func(str
 }
 
 // FastqChunkParserRope parses a FASTQ chunk directly from a rope without Pack().
-func FastqChunkParserRope(source string, rope *PieceOfChunk, quality_shift byte, with_quality, UtoT bool) (obiseq.BioSequenceSlice, error) {
+func FastqChunkParserRope(source string, rope *PieceOfChunk, quality_shift byte, with_quality, UtoT bool, fileName string) (obiseq.BioSequenceSlice, error) {
 	scanner := newRopeScanner(rope)
 	sequences := obiseq.MakeBioSequenceSlice(100)[:0]
 
@@ -334,7 +334,7 @@ func FastqChunkParserRope(source string, rope *PieceOfChunk, quality_shift byte,
 		// Line 2: sequence
 		sline := scanner.ReadLine()
 		if sline == nil {
-			log.Fatalf("@%s[%s]: unexpected EOF after header", id, source)
+			log.Fatalf("file %s: record @%s is truncated (header line with no sequence line following) — the FASTQ file appears incomplete", fileName, id)
 		}
 		seqDest := make([]byte, len(sline))
 		w := 0
@@ -350,7 +350,7 @@ func FastqChunkParserRope(source string, rope *PieceOfChunk, quality_shift byte,
 		}
 		seqDest = seqDest[:w]
 		if len(seqDest) == 0 {
-			log.Fatalf("@%s[%s]: sequence is empty", id, source)
+			log.Fatalf("file %s: record @%s has an empty sequence line", fileName, id)
 		}
 
 		// Line 3: + (skip)
@@ -382,16 +382,17 @@ func _ParseFastqFile(
 	out obiiter.IBioSequence,
 	quality_shift byte,
 	with_quality, UtoT bool,
+	fileName string,
 ) {
 
-	parser := FastqChunkParser(quality_shift, with_quality, UtoT)
+	parser := FastqChunkParser(quality_shift, with_quality, UtoT, fileName)
 
 	for chunks := range input {
 		var sequences obiseq.BioSequenceSlice
 		var err error
 
 		if chunks.Rope != nil {
-			sequences, err = FastqChunkParserRope(chunks.Source, chunks.Rope, quality_shift, with_quality, UtoT)
+			sequences, err = FastqChunkParserRope(chunks.Source, chunks.Rope, quality_shift, with_quality, UtoT, fileName)
 		} else {
 			sequences, err = parser(chunks.Source, chunks.Raw)
 		}
@@ -423,6 +424,8 @@ func ReadFastq(reader io.Reader, options ...WithOption) (obiiter.IBioSequence, e
 		false,
 	)
 
+	fileName := opt.FileName()
+
 	for i := 0; i < nworker; i++ {
 		out.Add(1)
 		go _ParseFastqFile(
@@ -431,6 +434,7 @@ func ReadFastq(reader io.Reader, options ...WithOption) (obiiter.IBioSequence, e
 			obidefault.ReadQualitiesShift(),
 			opt.ReadQualities(),
 			opt.UtoT(),
+			fileName,
 		)
 	}
 
@@ -456,7 +460,9 @@ func ReadFastq(reader io.Reader, options ...WithOption) (obiiter.IBioSequence, e
 }
 
 func ReadFastqFromFile(filename string, options ...WithOption) (obiiter.IBioSequence, error) {
-	options = append(options, OptionsSource(obiutils.RemoveAllExt((path.Base(filename)))))
+	options = append(options,
+		OptionsSource(obiutils.RemoveAllExt((path.Base(filename)))),
+		OptionsFileName(filename))
 
 	file, err := obiutils.Ropen(filename)
 
diff --git a/pkg/obiformats/options.go b/pkg/obiformats/options.go
index 8190801..e0c4525 100644
--- a/pkg/obiformats/options.go
+++ b/pkg/obiformats/options.go
@@ -35,6 +35,7 @@ type __options__ struct {
 	csv_auto              bool
 	paired_filename       string
 	source                string
+	filename              string
 	with_feature_table    bool
 	with_pattern          bool
 	with_parent           bool
@@ -216,6 +217,16 @@ func (opt Options) Source() string {
 	return opt.pointer.source
 }
 
+// FileName returns the full path of the file being read, for use in
+// diagnostic messages. It falls back to Source() when no explicit
+// file name has been set (e.g. reading from stdin or a raw reader).
+func (opt Options) FileName() string {
+	if opt.pointer.filename == "" {
+		return opt.pointer.source
+	}
+	return opt.pointer.filename
+}
+
 func (opt Options) WithFeatureTable() bool {
 	return opt.pointer.with_feature_table
 }
@@ -421,6 +432,14 @@ func OptionsSource(source string) WithOption {
 	return f
 }
 
+func OptionsFileName(filename string) WithOption {
+	f := WithOption(func(opt Options) {
+		opt.pointer.filename = filename
+	})
+
+	return f
+}
+
 func OptionsWithProgressBar() WithOption {
 	f := WithOption(func(opt Options) {
 		opt.pointer.with_progress_bar = true