diff --git a/sam.c b/sam.c
index e39ec3f85..7e58da6e7 100644
--- a/sam.c
+++ b/sam.c
@@ -2947,7 +2947,7 @@ int sam_parse1(kstring_t *s, sam_hdr_t *h, bam1_t *b)
     } else c->tid = -1;
 
     // pos
-    c->pos = hts_str2uint(p, &p, 63, &overflow) - 1;
+    c->pos = hts_str2uint(p, &p, 62, &overflow) - 1;
     if (*p++ != '\t') goto err_ret;
     if (c->pos < 0 && c->tid >= 0) {
         _parse_warn(1, "mapped query cannot have zero coordinate; treated as unmapped");
@@ -2990,15 +2990,16 @@ int sam_parse1(kstring_t *s, sam_hdr_t *h, bam1_t *b)
         _parse_warn(c->mtid < 0, "unrecognized mate reference name %s; treated as unmapped", hts_strprint(logbuf, sizeof logbuf, '"', q, SIZE_MAX));
     }
     // mpos
-    c->mpos = hts_str2uint(p, &p, 63, &overflow) - 1;
+    c->mpos = hts_str2uint(p, &p, 62, &overflow) - 1;
     if (*p++ != '\t') goto err_ret;
     if (c->mpos < 0 && c->mtid >= 0) {
         _parse_warn(1, "mapped mate cannot have zero coordinate; treated as unmapped");
         c->mtid = -1;
     }
     // tlen
-    c->isize = hts_str2int(p, &p, 64, &overflow);
+    c->isize = hts_str2int(p, &p, 63, &overflow);
     if (*p++ != '\t') goto err_ret;
+    _parse_err(overflow, "number outside allowed range");
     // seq
     q = _read_token(p);
     if (strcmp(q, "*")) {
diff --git a/test/sam.c b/test/sam.c
index 09e4aecf5..74591fc2d 100644
--- a/test/sam.c
+++ b/test/sam.c
@@ -1,6 +1,6 @@
 /*  test/sam.c -- SAM/BAM/CRAM API test cases.
 
-    Copyright (C) 2014-2020, 2022-2023 Genome Research Ltd.
+    Copyright (C) 2014-2020, 2022-2024 Genome Research Ltd.
 
     Author: John Marshall <jm18@sanger.ac.uk>
 
@@ -1408,16 +1408,16 @@ static void check_big_ref(int parse_header)
         "@HD\tVN:1.4\n"
         "@SQ\tSN:large#1\tLN:5000000000\n"
         "@SQ\tSN:small#1\tLN:100\n"
-        "@SQ\tSN:large#2\tLN:9223372034707292158\n"
+        "@SQ\tSN:large#2\tLN:4611686018427387904\n"
         "@SQ\tSN:small#2\tLN:1\n"
         "r1\t0\tlarge#1\t4999999000\t50\t8M\t*\t0\t0\tACGTACGT\tabcdefgh\n"
         "r2\t0\tsmall#1\t1\t50\t8M\t*\t0\t0\tACGTACGT\tabcdefgh\n"
-        "r3\t0\tlarge#2\t9223372034707292000\t50\t8M\t*\t0\t0\tACGTACGT\tabcdefgh\n"
-        "p1\t99\tlarge#2\t1\t50\t8M\t=\t9223372034707292150\t9223372034707292158\tACGTACGT\tabcdefgh\n"
-        "p1\t147\tlarge#2\t9223372034707292150\t50\t8M\t=\t1\t-9223372034707292158\tACGTACGT\tabcdefgh\n"
+        "r3\t0\tlarge#2\t4611686018427387000\t50\t8M\t*\t0\t0\tACGTACGT\tabcdefgh\n"
+        "p1\t99\tlarge#2\t1\t50\t8M\t=\t4611686018427387895\t4611686018427387903\tACGTACGT\tabcdefgh\n"
+        "p1\t147\tlarge#2\t4611686018427387895\t50\t8M\t=\t1\t-4611686018427387903\tACGTACGT\tabcdefgh\n"
         "r4\t0\tsmall#2\t2\t50\t8M\t*\t0\t0\tACGTACGT\tabcdefgh\n";
     const hts_pos_t expected_lengths[] = {
-        5000000000LL, 100LL, 9223372034707292158LL, 1LL
+        5000000000LL, 100LL, 4611686018427387904LL, 1LL
     };
     const int expected_tids[] = {
         0, 1, 2, 2, 2, 3
@@ -1426,11 +1426,11 @@ static void check_big_ref(int parse_header)
         -1, -1, -1, 2, 2, -1
     };
     const hts_pos_t expected_positions[] = {
-        4999999000LL - 1, 1LL - 1, 9223372034707292000LL - 1, 1LL - 1,
-        9223372034707292150LL - 1, 2LL - 1
+        4999999000LL - 1, 1LL - 1, 4611686018427387000LL - 1, 1LL - 1,
+        4611686018427387895LL - 1, 2LL - 1
     };
     const hts_pos_t expected_mpos[] = {
-        -1, -1, -1, 9223372034707292150LL - 1, 1LL - 1, -1
+        -1, -1, -1, 4611686018427387895LL - 1, 1LL - 1, -1
     };
     samFile *in = NULL, *out = NULL;
     sam_hdr_t *header = NULL, *dup_header = NULL;
diff --git a/vcf.c b/vcf.c
index daedad34d..7ce306f92 100644
--- a/vcf.c
+++ b/vcf.c
@@ -3703,7 +3703,7 @@ int vcf_parse(kstring_t *s, const bcf_hdr_t *h, bcf1_t *v)
 
     overflow = 0;
     char *tmp = p;
-    v->pos = hts_str2uint(p, &p, 63, &overflow);
+    v->pos = hts_str2uint(p, &p, 62, &overflow);
     if (overflow) {
         hts_log_error("Position value '%s' is too large", tmp);
         goto err;