diff --git a/bwape.c b/bwape.c
index 2a7f46ef..7dc3d740 100644
--- a/bwape.c
+++ b/bwape.c
@@ -633,7 +633,7 @@ void bwa_sai2sam_pe_core(const char *prefix, char *const fn_sa[2], char *const f
 	gap_opt_t opt, opt0;
 	khint_t iter;
 	isize_info_t last_ii; // this is for the last batch of reads
-	char str[1024];
+	char str[1024], magic[2][4];
 	bwt_t *bwt;
 	uint8_t *pac;
 
@@ -648,6 +648,12 @@ void bwa_sai2sam_pe_core(const char *prefix, char *const fn_sa[2], char *const f
 	g_hash = kh_init(b128);
 	last_ii.avg = -1.0;
 
+	err_fread_noeof(magic[0], 1, 4, fp_sa[0]);
+	err_fread_noeof(magic[1], 1, 4, fp_sa[1]);
+	if (strncmp(magic[0], SAI_MAGIC, 4) != 0 || strncmp(magic[1], SAI_MAGIC, 4) != 0) {
+		fprintf(stderr, "[E::%s] Unmatched SAI magic. Please re-run `aln' with the same version of bwa.\n", __func__);
+		exit(1);
+	}
 	err_fread_noeof(&opt, sizeof(gap_opt_t), 1, fp_sa[0]);
 	ks[0] = bwa_open_reads(opt.mode, fn_fa[0]);
 	opt0 = opt;
diff --git a/bwase.c b/bwase.c
index 85165d64..dcf29bfa 100644
--- a/bwase.c
+++ b/bwase.c
@@ -4,6 +4,7 @@
 #include <stdlib.h>
 #include <math.h>
 #include <time.h>
+#include <assert.h>
 #include "bwase.h"
 #include "bwtaln.h"
 #include "bntseq.h"
@@ -36,6 +37,7 @@ void bwa_aln2seq_core(int n_aln, const bwt_aln1_t *aln, bwa_seq_t *s, int set_ma
 			if (p->score > best) break;
 			if (drand48() * (p->l - p->k + 1 + cnt) > (double)cnt) {
 				s->n_mm = p->n_mm; s->n_gapo = p->n_gapo; s->n_gape = p->n_gape;
+				s->ref_shift = (int)p->n_del - (int)p->n_ins;
 				s->score = p->score;
 				s->sa = p->k + (bwtint_t)((p->l - p->k + 1) * drand48());
 			}
@@ -71,6 +73,7 @@ void bwa_aln2seq_core(int n_aln, const bwt_aln1_t *aln, bwa_seq_t *s, int set_ma
 				for (l = q->k; l <= q->l; ++l) {
 					s->multi[z].pos = l;
 					s->multi[z].gap = q->n_gapo + q->n_gape;
+					s->multi[z].ref_shift = (int)q->n_del - (int)q->n_ins;
 					s->multi[z++].mm = q->n_mm;
 				}
 				rest -= q->l - q->k + 1;
@@ -81,6 +84,7 @@ void bwa_aln2seq_core(int n_aln, const bwt_aln1_t *aln, bwa_seq_t *s, int set_ma
 					while (x < p) p -= p * j / (i--);
 					s->multi[z].pos = q->l - i;
 					s->multi[z].gap = q->n_gapo + q->n_gape;
+					s->multi[z].ref_shift = (int)q->n_del - (int)q->n_ins;
 					s->multi[z++].mm = q->n_mm;
 				}
 				rest = 0;
@@ -107,16 +111,15 @@ int bwa_approx_mapQ(const bwa_seq_t *p, int mm)
 	return (23 < g_log_n[n])? 0 : 23 - g_log_n[n];
 }
 
-bwtint_t bwa_sa2pos(const bntseq_t *bns, const bwt_t *bwt, bwtint_t sapos, int len, int *strand)
+bwtint_t bwa_sa2pos(const bntseq_t *bns, const bwt_t *bwt, bwtint_t sapos, int ref_len, int *strand)
 {
 	bwtint_t pos_f;
 	int is_rev;
-	pos_f = bns_depos(bns, bwt_sa(bwt, sapos), &is_rev); // pos_f
+	pos_f = bwt_sa(bwt, sapos); // position on the forward-reverse coordinate
+	if (pos_f < bns->l_pac && bns->l_pac < pos_f + ref_len) return (bwtint_t)-1;
+	pos_f = bns_depos(bns, pos_f, &is_rev); // position on the forward strand; this may be the first base or the last base
 	*strand = !is_rev;
-	/* NB: For gapped alignment, pacpos may not be correct, which will be fixed
-	 * in bwa_refine_gapped_core(). This line also determines the way "x" is
-	 * calculated in bwa_refine_gapped_core() when (ext < 0 && is_end == 0). */
-	if (is_rev) pos_f = pos_f + 1 < len? 0 : pos_f - len + 1; // mapped to the forward strand
+	if (is_rev) pos_f = pos_f + 1 < ref_len? 0 : pos_f - ref_len + 1; // position of the first base
 	return pos_f; // FIXME: it is possible that pos_f < bns->anns[ref_id].offset
 }
 
@@ -132,9 +135,11 @@ void bwa_cal_pac_pos_core(const bntseq_t *bns, const bwt_t *bwt, bwa_seq_t *seq,
 	if (seq->type != BWA_TYPE_UNIQUE && seq->type != BWA_TYPE_REPEAT) return;
 	max_diff = fnr > 0.0? bwa_cal_maxdiff(seq->len, BWA_AVG_ERR, fnr) : max_mm;
 	seq->seQ = seq->mapQ = bwa_approx_mapQ(seq, max_diff);
-	seq->pos = bwa_sa2pos(bns, bwt, seq->sa, seq->len, &strand);
+	//fprintf(stderr, "%d\n", seq->ref_shift);
+	seq->pos = bwa_sa2pos(bns, bwt, seq->sa, seq->len + seq->ref_shift, &strand);
 	seq->strand = strand;
 	seq->seQ = seq->mapQ = bwa_approx_mapQ(seq, max_diff);
+	if (seq->pos == (bwtint_t)-1) seq->type = BWA_TYPE_NO_MATCH;
 }
 
 void bwa_cal_pac_pos(const bntseq_t *bns, const char *prefix, int n_seqs, bwa_seq_t *seqs, int max_mm, float fnr)
@@ -150,9 +155,9 @@ void bwa_cal_pac_pos(const bntseq_t *bns, const char *prefix, int n_seqs, bwa_se
 		bwa_cal_pac_pos_core(bns, bwt, p, max_mm, fnr);
 		for (j = n_multi = 0; j < p->n_multi; ++j) {
 			bwt_multi1_t *q = p->multi + j;
-			q->pos = bwa_sa2pos(bns, bwt, q->pos, p->len, &strand);
+			q->pos = bwa_sa2pos(bns, bwt, q->pos, p->len + p->ref_shift, &strand);
 			q->strand = strand;
-			if (q->pos != p->pos)
+			if (q->pos != p->pos && q->pos != (bwtint_t)-1)
 				p->multi[n_multi++] = *q;
 		}
 		p->n_multi = n_multi;
@@ -162,64 +167,25 @@ void bwa_cal_pac_pos(const bntseq_t *bns, const char *prefix, int n_seqs, bwa_se
 
 #define SW_BW 50
 
-bwa_cigar_t *bwa_refine_gapped_core(bwtint_t l_pac, const ubyte_t *pacseq, int len, ubyte_t *seq, bwtint_t *_pos, int *n_cigar, int is_rev)
+bwa_cigar_t *bwa_refine_gapped_core(bwtint_t l_pac, const ubyte_t *pacseq, int len, ubyte_t *seq, int ref_shift, bwtint_t rb, int *n_cigar)
 {
 	bwa_cigar_t *cigar = 0;
 	uint32_t *cigar32 = 0;
 	ubyte_t *rseq;
-	int tle, qle, gtle, gscore;
-	int64_t k, rb, re, rlen;
+	int64_t k, re, rlen;
 	int8_t mat[25];
 
 	bwa_fill_scmat(1, 3, mat);
-	if (!is_rev) { // forward strand, the end position is correct
-		re = *_pos + len;
-		if (re > l_pac) re = l_pac;
-		rb = re - (len + SW_BW);
-		if (rb < 0) rb = 0;
-		rseq = bns_get_seq(l_pac, pacseq, rb, re, &rlen);
-		seq_reverse(len, seq, 0); // as we need to do left extension, we have to reverse both query and reference sequences
-		seq_reverse(rlen, rseq, 0);
-		ksw_extend(len, seq, rlen, rseq, 5, mat, 5, 1, SW_BW, 0, -1, len<<1, &qle, &tle, &gtle, &gscore, 0);
-		if (gscore > 0) tle = gtle, qle = len;
-		rb = re - tle; rlen = tle;
-		seq_reverse(len, seq, 0);
-		seq_reverse(rlen, rseq, 0);
-		if (rlen == 0) goto refine_gapped_err;
-		ksw_global(qle, &seq[len-qle], rlen, rseq, 5, mat, 5, 1, SW_BW, n_cigar, &cigar32);
-		if (qle < len) { // write soft clip
-			cigar = realloc(cigar, (*n_cigar + 1) * 4);
-			memmove(cigar + 1, cigar, *n_cigar * 4);
-			cigar[0] = (len - qle)<<4 | FROM_S;
-			++(*n_cigar);
-		}
-	} else { // reverse strand, the start position is correct
-		rb = *_pos; re = rb + len + SW_BW;
-		if (re > l_pac) re = l_pac;
-		rseq = bns_get_seq(l_pac, pacseq, rb, re, &rlen);
-		ksw_extend(len, seq, rlen, rseq, 5, mat, 5, 1, SW_BW, 0, -1, len<<1, &qle, &tle, &gtle, &gscore, 0);
-		if (gscore > 0) tle = gtle, qle = len;
-		re = rb + tle; rlen = tle;
-		if (rlen == 0) goto refine_gapped_err;
-		ksw_global(qle, seq, rlen, rseq, 5, mat, 5, 1, SW_BW, n_cigar, &cigar32); // right extension
-		if (qle < len) {
-			cigar = realloc(cigar, (*n_cigar + 1) * 4);
-			cigar[*n_cigar - 1] = (len - qle)<<4 | FROM_S;
-			++(*n_cigar);
-		}
-	}
-	*_pos = rb;
-
+	re = rb + len + ref_shift;
+	assert(re <= l_pac);
+	rseq = bns_get_seq(l_pac, pacseq, rb, re, &rlen);
+	assert(re - rb == rlen);
+	ksw_global(len, seq, rlen, rseq, 5, mat, 5, 1, SW_BW, n_cigar, &cigar32); // right extension
 	cigar = (bwa_cigar_t*)cigar32;
 	for (k = 0; k < *n_cigar; ++k)
 		cigar[k] = __cigar_create((cigar32[k]&0xf), (cigar32[k]>>4));
 	free(rseq);
 	return cigar;
-
-refine_gapped_err:
-	free(rseq);
-	*n_cigar = 0;
-	return 0;
 }
 
 char *bwa_cal_md1(int n_cigar, bwa_cigar_t *cigar, int len, bwtint_t pos, ubyte_t *seq,
@@ -311,7 +277,7 @@ void bwa_correct_trimmed(bwa_seq_t *s)
 void bwa_refine_gapped(const bntseq_t *bns, int n_seqs, bwa_seq_t *seqs, ubyte_t *_pacseq)
 {
 	ubyte_t *pacseq;
-	int i, j;
+	int i, j, k;
 	kstring_t *str;
 
 	if (!_pacseq) {
@@ -322,15 +288,18 @@ void bwa_refine_gapped(const bntseq_t *bns, int n_seqs, bwa_seq_t *seqs, ubyte_t
 	for (i = 0; i != n_seqs; ++i) {
 		bwa_seq_t *s = seqs + i;
 		seq_reverse(s->len, s->seq, 0); // IMPORTANT: s->seq is reversed here!!!
-		for (j = 0; j < s->n_multi; ++j) {
+		for (j = k = 0; j < s->n_multi; ++j) {
 			bwt_multi1_t *q = s->multi + j;
 			int n_cigar;
-			if (q->gap == 0) continue;
-			q->cigar = bwa_refine_gapped_core(bns->l_pac, pacseq, s->len, q->strand? s->rseq : s->seq, &q->pos, &n_cigar, q->strand);
-			q->n_cigar = n_cigar;
+			if (q->gap) { // gapped alignment
+				q->cigar = bwa_refine_gapped_core(bns->l_pac, pacseq, s->len, q->strand? s->rseq : s->seq, q->ref_shift, q->pos, &n_cigar);
+				q->n_cigar = n_cigar;
+				if (q->cigar) s->multi[k++] = *q;
+			} else s->multi[k++] = *q;
 		}
+		s->n_multi = k; // this squeezes out gapped alignments which failed the CIGAR generation
 		if (s->type == BWA_TYPE_NO_MATCH || s->type == BWA_TYPE_MATESW || s->n_gapo == 0) continue;
-		s->cigar = bwa_refine_gapped_core(bns->l_pac, pacseq, s->len, s->strand? s->rseq : s->seq, &s->pos, &s->n_cigar, s->strand);
+		s->cigar = bwa_refine_gapped_core(bns->l_pac, pacseq, s->len, s->strand? s->rseq : s->seq, s->ref_shift, s->pos, &s->n_cigar);
 		if (s->cigar == 0) s->type = BWA_TYPE_NO_MATCH;
 	}
 	// generate MD tag
@@ -339,8 +308,7 @@ void bwa_refine_gapped(const bntseq_t *bns, int n_seqs, bwa_seq_t *seqs, ubyte_t
 		bwa_seq_t *s = seqs + i;
 		if (s->type != BWA_TYPE_NO_MATCH) {
 			int nm;
-			s->md = bwa_cal_md1(s->n_cigar, s->cigar, s->len, s->pos, s->strand? s->rseq : s->seq,
-								bns->l_pac, pacseq, str, &nm);
+			s->md = bwa_cal_md1(s->n_cigar, s->cigar, s->len, s->pos, s->strand? s->rseq : s->seq, bns->l_pac, pacseq, str, &nm);
 			s->nm = nm;
 		}
 	}
@@ -487,7 +455,6 @@ void bwa_print_sam1(const bntseq_t *bns, bwa_seq_t *p, const bwa_seq_t *mate, in
 				for (i = 0; i < p->n_multi; ++i) {
 					bwt_multi1_t *q = p->multi + i;
 					int k;
-					if (q->cigar == 0) continue;
 					j = pos_end_multi(q, p->len) - q->pos;
 					nn = bns_cnt_ambi(bns, q->pos, j, &seqid);
 					err_printf("%s,%c%d,", bns->anns[seqid].name, q->strand? '-' : '+',
@@ -538,6 +505,7 @@ void bwa_sai2sam_se_core(const char *prefix, const char *fn_sa, const char *fn_f
 	bntseq_t *bns;
 	FILE *fp_sa;
 	gap_opt_t opt;
+	char magic[4];
 
 	// initialization
 	bwase_initialize();
@@ -546,6 +514,11 @@ void bwa_sai2sam_se_core(const char *prefix, const char *fn_sa, const char *fn_f
 	fp_sa = xopen(fn_sa, "r");
 
 	m_aln = 0;
+	err_fread_noeof(magic, 1, 4, fp_sa);
+	if (strncmp(magic, SAI_MAGIC, 4) != 0) {
+		fprintf(stderr, "[E::%s] Unmatched SAI magic. Please re-run `aln' with the same version of bwa.\n", __func__);
+		exit(1);
+	}
 	err_fread_noeof(&opt, sizeof(gap_opt_t), 1, fp_sa);
 	bwa_print_sam_hdr(bns, rg_line);
 	//bwa_print_sam_PG();
diff --git a/bwtaln.c b/bwtaln.c
index e7727924..68d0274a 100644
--- a/bwtaln.c
+++ b/bwtaln.c
@@ -116,6 +116,7 @@ void bwa_cal_sa_reg_gap(int tid, bwt_t *const bwt, int n_seqs, bwa_seq_t *seqs,
 		for (j = 0; j < p->len; ++j) // we need to complement
 			p->seq[j] = p->seq[j] > 3? 4 : 3 - p->seq[j];
 		p->aln = bwt_match_gap(bwt, p->len, p->seq, w, p->len <= opt->seed_len? 0 : seed_w, &local_opt, &p->n_aln, stack);
+		//fprintf(stderr, "mm=%lld,ins=%lld,del=%lld,gapo=%lld\n", p->aln->n_mm, p->aln->n_ins, p->aln->n_del, p->aln->n_gapo);
 		// clean up the unused data in the record
 		free(p->name); free(p->seq); free(p->rseq); free(p->qual);
 		p->name = 0; p->seq = p->rseq = p->qual = 0;
@@ -173,6 +174,7 @@ void bwa_aln_core(const char *prefix, const char *fn_fa, const gap_opt_t *opt)
 	}
 
 	// core loop
+	err_fwrite(SAI_MAGIC, 1, 4, stdout);
 	err_fwrite(opt, sizeof(gap_opt_t), 1, stdout);
 	while ((seqs = bwa_read_seq(ks, 0x40000, &n_seqs, opt->mode, opt->trim_qual)) != 0) {
 		tot_seqs += n_seqs;
diff --git a/bwtaln.h b/bwtaln.h
index 556f2593..4616ff5a 100644
--- a/bwtaln.h
+++ b/bwtaln.h
@@ -33,14 +33,15 @@
 #define FROM_D 2
 #define FROM_S 3
 
+#define SAI_MAGIC "SAI\1"
+
 typedef struct {
 	bwtint_t w;
 	int bid;
 } bwt_width_t;
 
 typedef struct {
-	uint32_t n_mm:16, n_gapo:8, n_gape:8;
-	int score;
+	uint64_t n_mm:8, n_gapo:8, n_gape:8, score:20, n_ins:10, n_del:10;
 	bwtint_t k, l;
 } bwt_aln1_t;
 
@@ -57,6 +58,7 @@ typedef uint16_t bwa_cigar_t;
 
 typedef struct {
 	uint32_t n_cigar:15, gap:8, mm:8, strand:1;
+	int ref_shift;
 	bwtint_t pos;
 	bwa_cigar_t *cigar;
 } bwt_multi1_t;
@@ -77,6 +79,7 @@ typedef struct {
 	// alignment information
 	bwtint_t sa, pos;
 	uint64_t c1:28, c2:28, seQ:8; // number of top1 and top2 hits; single-end mapQ
+	int ref_shift;
 	int n_cigar;
 	bwa_cigar_t *cigar;
 	// for multi-threading only
diff --git a/bwtgap.c b/bwtgap.c
index 16d90255..08bc1f48 100644
--- a/bwtgap.c
+++ b/bwtgap.c
@@ -45,7 +45,7 @@ static void gap_reset_stack(gap_stack_t *stack)
 	stack->n_entries = 0;
 }
 
-static inline void gap_push(gap_stack_t *stack, int i, bwtint_t k, bwtint_t l, int n_mm, int n_gapo, int n_gape,
+static inline void gap_push(gap_stack_t *stack, int i, bwtint_t k, bwtint_t l, int n_mm, int n_gapo, int n_gape, int n_ins, int n_del,
 							int state, int is_diff, const gap_opt_t *opt)
 {
 	int score;
@@ -59,7 +59,9 @@ static inline void gap_push(gap_stack_t *stack, int i, bwtint_t k, bwtint_t l, i
 	}
 	p = q->stack + q->n_entries;
 	p->info = (u_int32_t)score<<21 | i; p->k = k; p->l = l;
-	p->n_mm = n_mm; p->n_gapo = n_gapo; p->n_gape = n_gape; p->state = state;
+	p->n_mm = n_mm; p->n_gapo = n_gapo; p->n_gape = n_gape;
+	p->n_ins = n_ins; p->n_del = n_del;
+	p->state = state; 
 	p->last_diff_pos = is_diff? i : 0;
 	++(q->n_entries);
 	++(stack->n_entries);
@@ -106,7 +108,7 @@ static inline int int_log2(uint32_t v)
 
 bwt_aln1_t *bwt_match_gap(bwt_t *const bwt, int len, const ubyte_t *seq, bwt_width_t *width,
 						  bwt_width_t *seed_width, const gap_opt_t *opt, int *_n_aln, gap_stack_t *stack)
-{
+{ // $seq is the reverse complement of the input read
 	int best_score = aln_score(opt->max_diff+1, opt->max_gapo+1, opt->max_gape+1, opt);
 	int best_diff = opt->max_diff + 1, max_diff = opt->max_diff;
 	int best_cnt = 0;
@@ -126,7 +128,7 @@ bwt_aln1_t *bwt_match_gap(bwt_t *const bwt, int len, const ubyte_t *seq, bwt_wid
 
 	//for (j = 0; j != len; ++j) printf("#0 %d: [%d,%u]\t[%d,%u]\n", j, w[0][j].bid, w[0][j].w, w[1][j].bid, w[1][j].w);
 	gap_reset_stack(stack); // reset stack
-	gap_push(stack, len, 0, bwt->seq_len, 0, 0, 0, 0, 0, opt);
+	gap_push(stack, len, 0, bwt->seq_len, 0, 0, 0, 0, 0, 0, 0, opt);
 
 	while (stack->n_entries) {
 		gap_entry_t e;
@@ -186,8 +188,10 @@ bwt_aln1_t *bwt_match_gap(bwt_t *const bwt, int len, const ubyte_t *seq, bwt_wid
 				}
 				p = aln + n_aln;
 				p->n_mm = e.n_mm; p->n_gapo = e.n_gapo; p->n_gape = e.n_gape;
+				p->n_ins = e.n_ins; p->n_del = e.n_del;
 				p->k = k; p->l = l;
 				p->score = score;
+				//fprintf(stderr, "*** n_mm=%d,n_gapo=%d,n_gape=%d,n_ins=%d,n_del=%d\n", e.n_mm, e.n_gapo, e.n_gape, e.n_ins, e.n_del);
 				++n_aln;
 			}
 			continue;
@@ -214,24 +218,24 @@ bwt_aln1_t *bwt_match_gap(bwt_t *const bwt, int len, const ubyte_t *seq, bwt_wid
 			if (e.state == STATE_M) { // gap open
 				if (e.n_gapo < opt->max_gapo) { // gap open is allowed
 					// insertion
-					gap_push(stack, i, k, l, e.n_mm, e.n_gapo + 1, e.n_gape, STATE_I, 1, opt);
+					gap_push(stack, i, k, l, e.n_mm, e.n_gapo + 1, e.n_gape, e.n_ins + 1, e.n_del, STATE_I, 1, opt);
 					// deletion
 					for (j = 0; j != 4; ++j) {
 						k = bwt->L2[j] + cnt_k[j] + 1;
 						l = bwt->L2[j] + cnt_l[j];
-						if (k <= l) gap_push(stack, i + 1, k, l, e.n_mm, e.n_gapo + 1, e.n_gape, STATE_D, 1, opt);
+						if (k <= l) gap_push(stack, i + 1, k, l, e.n_mm, e.n_gapo + 1, e.n_gape, e.n_ins, e.n_del + 1, STATE_D, 1, opt);
 					}
 				}
 			} else if (e.state == STATE_I) { // extention of an insertion
 				if (e.n_gape < opt->max_gape) // gap extention is allowed
-					gap_push(stack, i, k, l, e.n_mm, e.n_gapo, e.n_gape + 1, STATE_I, 1, opt);
+					gap_push(stack, i, k, l, e.n_mm, e.n_gapo, e.n_gape + 1, e.n_ins + 1, e.n_del, STATE_I, 1, opt);
 			} else if (e.state == STATE_D) { // extention of a deletion
 				if (e.n_gape < opt->max_gape) { // gap extention is allowed
 					if (e.n_gape + e.n_gapo < max_diff || occ < opt->max_del_occ) {
 						for (j = 0; j != 4; ++j) {
 							k = bwt->L2[j] + cnt_k[j] + 1;
 							l = bwt->L2[j] + cnt_l[j];
-							if (k <= l) gap_push(stack, i + 1, k, l, e.n_mm, e.n_gapo, e.n_gape + 1, STATE_D, 1, opt);
+							if (k <= l) gap_push(stack, i + 1, k, l, e.n_mm, e.n_gapo, e.n_gape + 1, e.n_ins, e.n_del + 1, STATE_D, 1, opt);
 						}
 					}
 				}
@@ -244,13 +248,13 @@ bwt_aln1_t *bwt_match_gap(bwt_t *const bwt, int len, const ubyte_t *seq, bwt_wid
 				int is_mm = (j != 4 || seq[i] > 3);
 				k = bwt->L2[c] + cnt_k[c] + 1;
 				l = bwt->L2[c] + cnt_l[c];
-				if (k <= l) gap_push(stack, i, k, l, e.n_mm + is_mm, e.n_gapo, e.n_gape, STATE_M, is_mm, opt);
+				if (k <= l) gap_push(stack, i, k, l, e.n_mm + is_mm, e.n_gapo, e.n_gape, e.n_ins, e.n_del, STATE_M, is_mm, opt);
 			}
 		} else if (seq[i] < 4) { // try exact match only
 			int c = seq[i] & 3;
 			k = bwt->L2[c] + cnt_k[c] + 1;
 			l = bwt->L2[c] + cnt_l[c];
-			if (k <= l) gap_push(stack, i, k, l, e.n_mm, e.n_gapo, e.n_gape, STATE_M, 0, opt);
+			if (k <= l) gap_push(stack, i, k, l, e.n_mm, e.n_gapo, e.n_gape, e.n_ins, e.n_del, STATE_M, 0, opt);
 		}
 	}
 
diff --git a/bwtgap.h b/bwtgap.h
index 83987628..7dd61659 100644
--- a/bwtgap.h
+++ b/bwtgap.h
@@ -7,8 +7,9 @@
 typedef struct { // recursion stack
 	u_int32_t info; // score<<21 | i
 	u_int32_t n_mm:8, n_gapo:8, n_gape:8, state:2, n_seed_mm:6;
-	bwtint_t k, l; // (k,l) is the SA region of [i,n-1]
+	u_int32_t n_ins:16, n_del:16;
 	int last_diff_pos;
+	bwtint_t k, l; // (k,l) is the SA region of [i,n-1]
 } gap_entry_t;
 
 typedef struct {
diff --git a/main.c b/main.c
index 5e5a0242..d243144d 100644
--- a/main.c
+++ b/main.c
@@ -3,7 +3,7 @@
 #include "utils.h"
 
 #ifndef PACKAGE_VERSION
-#define PACKAGE_VERSION "0.7.4-r396-beta"
+#define PACKAGE_VERSION "0.7.4-r397-beta"
 #endif
 
 int bwa_fa2pac(int argc, char *argv[]);