diff --git a/miniprot.h b/miniprot.h
index a8ddd19..4c4cd0e 100644
--- a/miniprot.h
+++ b/miniprot.h
@@ -3,7 +3,7 @@
 
 #include <stdint.h>
 
-#define MP_VERSION "0.13-r260-dirty"
+#define MP_VERSION "0.13-r261-dirty"
 
 #define MP_F_NO_SPLICE    0x1
 #define MP_F_NO_ALIGN     0x2
diff --git a/nasw-sse.c b/nasw-sse.c
index 76aa19e..68fc7fd 100644
--- a/nasw-sse.c
+++ b/nasw-sse.c
@@ -127,8 +127,8 @@ static uint8_t *ns_prep_seq(void *km, const char *ns, int32_t nl, const char *as
 	if (ss) { // NB: ss[] uses the offset rule to specify a splice site; donor/acceptor[] uses a different rule. The ss[] way is better but too tricky to change now
 		for (i = 1; i < nl; ++i) {
 			if (ss[i]>>1 == 0) continue;
-			if (ss[i]&1) acceptor[i-1] -= (int8_t)(ss[i]>>1);
-			else donor[i-1] -= (int8_t)(ss[i]>>1);
+			if (ss[i]&1) acceptor[i-1] -= (int8_t)(ss[i]>>1) - (int8_t)NS_SPSC_OFFSET;
+			else donor[i-1] -= (int8_t)(ss[i]>>1) - (int8_t)NS_SPSC_OFFSET;
 		}
 	}
 	ns_prep_nas(ns, nl, opt, nas);
@@ -170,8 +170,8 @@ static uint8_t *ns_prep_seq_left(void *km, const char *ns, int32_t nl, const cha
 	if (ss) {
 		for (i = 0; i < nl; ++i) {
 			if (ss[i]>>1 == 0) continue;
-			if (ss[i]&1) donor[nl - i - 1] -= (int8_t)(ss[i]>>1);
-			else acceptor[nl - i - 1] -= (int8_t)(ss[i]>>1);
+			if (ss[i]&1) donor[nl - i - 1] -= (int8_t)(ss[i]>>1) - (int8_t)NS_SPSC_OFFSET;
+			else acceptor[nl - i - 1] -= (int8_t)(ss[i]>>1) - (int8_t)NS_SPSC_OFFSET;
 		}
 	}
 	ns_prep_nas(ns, nl, opt, nas);
diff --git a/nasw.h b/nasw.h
index 84492e4..510c468 100644
--- a/nasw.h
+++ b/nasw.h
@@ -51,6 +51,8 @@
 #define NS_S_GENERIC    1
 #define NS_S_MAMMAL     2
 
+#define NS_SPSC_OFFSET 64
+
 extern char *ns_tab_nt_i2c, *ns_tab_aa_i2c;
 extern uint8_t ns_tab_a2r[22], ns_tab_nt4[256], ns_tab_aa20[256], ns_tab_aa13[256];
 extern uint8_t ns_tab_codon[64], ns_tab_codon13[64];
diff --git a/ntseq.c b/ntseq.c
index a7a9f59..0709a20 100644
--- a/ntseq.c
+++ b/ntseq.c
@@ -242,6 +242,7 @@ int32_t mp_ntseq_read_spsc(mp_ntdb_t *nt, const char *fn, int32_t max_sc)
 
 	fp = fn && strcmp(fn, "-") != 0? gzopen(fn, "rb") : gzdopen(0, "rb");
 	if (fp == 0) return -1;
+	if (max_sc > 63) max_sc = 63;
 	mp_ntseq_index_name(nt);
 	nt->spsc = Kcalloc(0, mp_spsc_t, nt->n_ctg * 2);
 	ks = ks_init(fp);
@@ -271,15 +272,15 @@ int32_t mp_ntseq_read_spsc(mp_ntdb_t *nt, const char *fn, int32_t max_sc)
 			}
 		}
 		if (i < 4) continue; // not enough fields
-		if (score <= 0) continue;
 		if (score > max_sc) score = max_sc;
+		if (score < -max_sc) score = -max_sc;
 		cid = mp_ntseq_name2id(nt, name);
 		if (cid < 0 || type < 0 || strand == 0 || pos < 0) continue; // FIXME: give a warning!
 		s = &nt->spsc[cid << 1 | (strand > 0? 0 : 1)];
 		Kgrow(0, uint64_t, s->a, s->n, s->m);
 		if (strand < 0) pos = nt->ctg[cid].len - pos;
 		if (pos > 0 && pos < nt->ctg[cid].len) { // ignore scores at the ends
-			s->a[s->n++] = (uint64_t)pos<<8 | score<<1 | type;
+			s->a[s->n++] = (uint64_t)pos << 8 | (score + NS_SPSC_OFFSET) << 1 | type;
 			++n_read;
 		}
 	}