diff --git a/format.c b/format.c
index deadbe1..c6b7272 100644
--- a/format.c
+++ b/format.c
@@ -105,10 +105,15 @@ err_set_rg:
 	free(rg_line);
 }
 
-void mm_write_sam_hdr_no_SQ(const char *rg, const char *ver, int argc, char *argv[])
+void mm_write_sam_hdr(const mm_idx_t *idx, const char *rg, const char *ver, int argc, char *argv[])
 {
 	kstring_t str = {0,0,0};
-	sam_write_rg_line(&str, rg);
+	if (idx) {
+		uint32_t i;
+		for (i = 0; i < idx->n_seq; ++i)
+			printf("@SQ\tSN:%s\tLN:%d\n", idx->seq[i].name, idx->seq[i].len);
+	}
+	if (rg) sam_write_rg_line(&str, rg);
 	mm_sprintf_lite(&str, "@PG\tID:minimap2\tPN:minimap2");
 	if (ver) mm_sprintf_lite(&str, "\tVN:%s", ver);
 	if (argc > 1) {
@@ -213,13 +218,6 @@ void mm_write_paf(kstring_t *s, const mm_idx_t *mi, const mm_bseq1_t *t, const m
 		write_cs(km, s, mi, t, r);
 }
 
-void mm_write_sam_SQ(const mm_idx_t *idx)
-{
-	uint32_t i;
-	for (i = 0; i < idx->n_seq; ++i)
-		printf("@SQ\tSN:%s\tLN:%d\n", idx->seq[i].name, idx->seq[i].len);
-}
-
 static void sam_write_sq(kstring_t *s, char *seq, int l, int rev, int comp)
 {
 	extern unsigned char seq_comp_table[256];
diff --git a/index.c b/index.c
index 4bc4c35..00f212c 100644
--- a/index.c
+++ b/index.c
@@ -427,28 +427,28 @@ mm_idx_t *mm_idx_load(FILE *fp)
 	return mi;
 }
 
-int mm_idx_is_idx(const char *fn)
+int64_t mm_idx_is_idx(const char *fn)
 {
 	int fd, is_idx = 0;
-	off_t ret;
+	off_t ret, off_end;
 	char magic[4];
 
 	if (strcmp(fn, "-") == 0) return 0; // read from pipe; not an index
 	fd = open(fn, O_RDONLY);
 	if (fd < 0) return -1; // error
-	if ((ret = lseek(fd, 0, SEEK_END)) >= 4) {
+	if ((off_end = lseek(fd, 0, SEEK_END)) >= 4) {
 		lseek(fd, 0, SEEK_SET);
 		ret = read(fd, magic, 4);
 		if (ret == 4 && strncmp(magic, MM_IDX_MAGIC, 4) == 0)
 			is_idx = 1;
 	}
 	close(fd);
-	return is_idx;
+	return is_idx? off_end : 0;
 }
 
 mm_idx_reader_t *mm_idx_reader_open(const char *fn, const mm_idxopt_t *opt, const char *fn_out)
 {
-	int is_idx;
+	int64_t is_idx;
 	mm_idx_reader_t *r;
 	is_idx = mm_idx_is_idx(fn);
 	if (is_idx < 0) return 0; // failed to open the index
@@ -456,8 +456,10 @@ mm_idx_reader_t *mm_idx_reader_open(const char *fn, const mm_idxopt_t *opt, cons
 	r->is_idx = is_idx;
 	if (opt) r->opt = *opt;
 	else mm_idxopt_init(&r->opt);
-	if (r->is_idx) r->fp.idx = fopen(fn, "rb");
-	else r->fp.seq = mm_bseq_open(fn);
+	if (r->is_idx) {
+		r->fp.idx = fopen(fn, "rb");
+		r->idx_size = is_idx;
+	} else r->fp.seq = mm_bseq_open(fn);
 	if (fn_out) r->fp_out = fopen(fn_out, "wb");
 	return r;
 }
@@ -485,3 +487,8 @@ mm_idx_t *mm_idx_reader_read(mm_idx_reader_t *r, int n_threads)
 	}
 	return mi;
 }
+
+int mm_idx_reader_eof(const mm_idx_reader_t *r) // TODO: in extremely rare cases, mm_bseq_eof() might not work
+{
+	return r->is_idx? (feof(r->fp.idx) || ftell(r->fp.idx) == r->idx_size) : mm_bseq_eof(r->fp.seq);
+}
diff --git a/main.c b/main.c
index f56327c..43d6ee3 100644
--- a/main.c
+++ b/main.c
@@ -6,7 +6,7 @@
 #include "mmpriv.h"
 #include "getopt.h"
 
-#define MM_VERSION "2.2-r465-dirty"
+#define MM_VERSION "2.2-r466-dirty"
 
 #ifdef __linux__
 #include <sys/resource.h>
@@ -25,7 +25,7 @@ void liftrlimit() {}
 static struct option long_options[] = {
 	{ "bucket-bits",    required_argument, 0, 0 },
 	{ "mb-size",        required_argument, 0, 'K' },
-	{ "int-rname",      no_argument,       0, 0 }, // obsolete; kept as a placeholder
+	{ "seed",           required_argument, 0, 0 },
 	{ "no-kalloc",      no_argument,       0, 0 },
 	{ "print-qname",    no_argument,       0, 0 },
 	{ "no-self",        no_argument,       0, 0 },
@@ -35,11 +35,9 @@ static struct option long_options[] = {
 	{ "print-aln-seq",  no_argument,       0, 0 },
 	{ "splice",         no_argument,       0, 0 },
 	{ "cost-non-gt-ag", required_argument, 0, 0 },
-	{ "no-sam-sq",      no_argument,       0, 0 },
+	{ "no-long-join",   no_argument,       0, 0 },
 	{ "sr",             no_argument,       0, 0 },
 	{ "multi",          optional_argument, 0, 0 },
-	{ "no-long-join",   no_argument,       0, 0 },
-	{ "seed",           required_argument, 0, 0 },
 	{ "print-2nd",      optional_argument, 0, 0 },
 	{ "help",           no_argument,       0, 'h' },
 	{ "max-intron-len", required_argument, 0, 'G' },
@@ -119,6 +117,7 @@ int main(int argc, char *argv[])
 		else if (c == 'R') rg = optarg;
 		else if (c == 'h') fp_help = stdout;
 		else if (c == 0 && long_idx == 0) ipt.bucket_bits = atoi(optarg); // --bucket-bits
+		else if (c == 0 && long_idx == 2) opt.seed = atoi(optarg); // --seed
 		else if (c == 0 && long_idx == 3) mm_dbg_flag |= MM_DBG_NO_KALLOC; // --no-kalloc
 		else if (c == 0 && long_idx == 4) mm_dbg_flag |= MM_DBG_PRINT_QNAME; // --print-qname
 		else if (c == 0 && long_idx == 5) opt.flag |= MM_F_NO_SELF; // --no-self
@@ -128,15 +127,13 @@ int main(int argc, char *argv[])
 		else if (c == 0 && long_idx == 9) mm_dbg_flag |= MM_DBG_PRINT_QNAME | MM_DBG_PRINT_ALN_SEQ; // --print-aln-seq
 		else if (c == 0 && long_idx ==10) opt.flag |= MM_F_SPLICE; // --splice
 		else if (c == 0 && long_idx ==11) opt.noncan = atoi(optarg); // --cost-non-gt-ag
-		else if (c == 0 && long_idx ==12) opt.flag |= MM_F_NO_SAM_SQ; // --no-sam-sq
+		else if (c == 0 && long_idx ==12) opt.flag |= MM_F_NO_LJOIN; // --no-long-join
 		else if (c == 0 && long_idx ==13) opt.flag |= MM_F_SR; // --sr
-		else if (c == 0 && long_idx ==15) opt.flag |= MM_F_NO_LJOIN; // --no-long-join
-		else if (c == 0 && long_idx ==16) opt.seed = atoi(optarg); // --seed
 		else if (c == 0 && long_idx ==14) { // --multi
 			if (optarg == 0 || strcmp(optarg, "yes") == 0 || strcmp(optarg, "y") == 0)
 				opt.flag |= MM_F_MULTI_SEG;
 			else opt.flag &= ~MM_F_MULTI_SEG;
-		} else if (c == 0 && long_idx ==17) { // --print-2nd
+		} else if (c == 0 && long_idx ==15) { // --print-2nd
 			if (optarg == 0 || strcmp(optarg, "yes") == 0 || strcmp(optarg, "y") == 0)
 				opt.flag &= ~MM_F_NO_PRINT_2ND;
 			else opt.flag |= MM_F_NO_PRINT_2ND;
@@ -235,11 +232,16 @@ int main(int argc, char *argv[])
 		fprintf(stderr, "[ERROR] missing input: please specify a query file to map or option -d to keep the index\n");
 		return 1;
 	}
-	if (opt.flag & MM_F_OUT_SAM)
-		mm_write_sam_hdr_no_SQ(rg, MM_VERSION, argc, argv);
 	while ((mi = mm_idx_reader_read(idx_rdr, n_threads)) != 0) {
-		if (mm_verbose >= 2 && idx_rdr->n_parts > 1 && (opt.flag&MM_F_OUT_SAM) && !(opt.flag&MM_F_NO_SAM_SQ))
-			fprintf(stderr, "[WARNING] \033[1;31mSAM output is malformated due to internal @SQ lines. Please add option --no-sam-sq or filter afterwards.\033[0m\n");
+		if ((opt.flag & MM_F_OUT_SAM) && idx_rdr->n_parts == 1) {
+			if (mm_idx_reader_eof(idx_rdr)) {
+				mm_write_sam_hdr(mi, rg, MM_VERSION, argc, argv);
+			} else {
+				mm_write_sam_hdr(0, rg, MM_VERSION, argc, argv);
+				if (mm_verbose >= 2)
+					fprintf(stderr, "[WARNING] \033[1;31mFor a multi-part index, no @SQ lines will be outputted.\033[0m\n");
+			}
+		}
 		if (mm_verbose >= 3)
 			fprintf(stderr, "[M::%s::%.3f*%.2f] loaded/built the index for %d target sequence(s)\n",
 					__func__, realtime() - mm_realtime0, cputime() / (realtime() - mm_realtime0), mi->n_seq);
diff --git a/map.c b/map.c
index 38cbf15..8b5a9aa 100644
--- a/map.c
+++ b/map.c
@@ -500,8 +500,6 @@ int mm_map_file_multi_seg(const mm_idx_t *idx, int n_segs, const char **fn, cons
 	pl.opt = opt, pl.mi = idx;
 	pl.n_threads = n_threads > 1? n_threads : 1;
 	pl.mini_batch_size = opt->mini_batch_size;
-	if ((opt->flag & MM_F_OUT_SAM) && !(opt->flag & MM_F_NO_SAM_SQ))
-		mm_write_sam_SQ(idx);
 	kt_pipeline(n_threads == 1? 1 : 2, worker_pipeline, &pl, 3);
 	free(pl.str.s);
 	for (i = 0; i < n_segs; ++i)
diff --git a/minimap.h b/minimap.h
index 51a0742..47ae44f 100644
--- a/minimap.h
+++ b/minimap.h
@@ -16,7 +16,6 @@
 #define MM_F_SPLICE_FOR  0x100 // match GT-AG
 #define MM_F_SPLICE_REV  0x200 // match CT-AC, the reverse complement of GT-AG
 #define MM_F_NO_LJOIN    0x400
-#define MM_F_NO_SAM_SQ   0x800
 #define MM_F_SR          0x1000
 #define MM_F_MULTI_SEG   0x2000
 #define MM_F_NO_PRINT_2ND  0x4000
@@ -116,6 +115,7 @@ typedef struct {
 // index reader
 typedef struct {
 	int is_idx, n_parts;
+	int64_t idx_size;
 	mm_idxopt_t opt;
 	FILE *fp_out;
 	union {
@@ -189,6 +189,8 @@ mm_idx_t *mm_idx_reader_read(mm_idx_reader_t *r, int n_threads);
  */
 void mm_idx_reader_close(mm_idx_reader_t *r);
 
+int mm_idx_reader_eof(const mm_idx_reader_t *r);
+
 /**
  * Print index statistics to stderr
  *
diff --git a/minimap2.1 b/minimap2.1
index 3bd5191..6ab8112 100644
--- a/minimap2.1
+++ b/minimap2.1
@@ -257,11 +257,6 @@ use
 .TP
 .B --version
 Print version number to stdout
-.TP
-.B --no-sam-hdr
-Don't output SAM header lines. Use this option if the index consists of
-multiple parts; otherwise the SAM output is malformated due to internal header
-lines.
 .SS Preset options
 .TP 10
 .BI -x \ STR
diff --git a/mmpriv.h b/mmpriv.h
index 6806a6b..a48a480 100644
--- a/mmpriv.h
+++ b/mmpriv.h
@@ -54,8 +54,7 @@ uint32_t ks_ksmall_uint32_t(size_t n, uint32_t arr[], size_t kk);
 
 void mm_sketch(void *km, const char *str, int len, int w, int k, uint32_t rid, int is_hpc, mm128_v *p);
 
-void mm_write_sam_SQ(const mm_idx_t *idx);
-void mm_write_sam_hdr_no_SQ(const char *rg, const char *ver, int argc, char *argv[]);
+void mm_write_sam_hdr(const mm_idx_t *mi, const char *rg, const char *ver, int argc, char *argv[]);
 void mm_write_paf(kstring_t *s, const mm_idx_t *mi, const mm_bseq1_t *t, const mm_reg1_t *r, void *km, int opt_flag);
 void mm_write_sam(kstring_t *s, const mm_idx_t *mi, const mm_bseq1_t *t, const mm_reg1_t *r, int n_regs, const mm_reg1_t *regs);