diff --git a/include/osmocom/core/bitvec.h b/include/osmocom/core/bitvec.h
index d64d69d..a7e6fc4 100644
--- a/include/osmocom/core/bitvec.h
+++ b/include/osmocom/core/bitvec.h
@@ -80,7 +80,7 @@
 int bitvec_unhex(struct bitvec *bv, const char *src);
 unsigned int bitvec_pack(const struct bitvec *bv, uint8_t *buffer);
 unsigned int bitvec_unpack(struct bitvec *bv, const uint8_t *buffer);
-uint64_t bitvec_read_field(struct bitvec *bv, unsigned int read_index, unsigned int len);
-int bitvec_write_field(struct bitvec *bv, unsigned int write_index, uint64_t val, unsigned int len);
+uint64_t bitvec_read_field(struct bitvec *bv, unsigned int *read_index, unsigned int len);
+int bitvec_write_field(struct bitvec *bv, unsigned int *write_index, uint64_t val, unsigned int len);
 
 /*! @} */
diff --git a/src/bitvec.c b/src/bitvec.c
index 46e83f3..b5d2c24 100644
--- a/src/bitvec.c
+++ b/src/bitvec.c
@@ -394,22 +394,22 @@
 		if (sscanf(src + i, "%1x", &val) < 1) {
 			return 1;
 		}
-		bitvec_write_field(bv, write_index,val, 4);
+		bitvec_write_field(bv, &write_index, val, 4);
 	}
 	return 0;
 }
 
 /*! \brief read part of the vector
  *  \param[in] bv The boolean vector to work on
- *  \param[in] read_index Where reading supposed to start in the vector
+ *  \param[in,out] read_index Where reading supposed to start in the vector
  *  \param[in] len How many bits to read from vector
  *  \returns read bits or negative value on error
  */
-uint64_t bitvec_read_field(struct bitvec *bv, unsigned int read_index, unsigned int len)
+uint64_t bitvec_read_field(struct bitvec *bv, unsigned int *read_index, unsigned int len)
 {
 	unsigned int i;
 	uint64_t ui = 0;
-	bv->cur_bit = read_index;
+	bv->cur_bit = *read_index;
 
 	for (i = 0; i < len; i++) {
 		int bit = bitvec_get_bit_pos((const struct bitvec *)bv, bv->cur_bit);
@@ -419,21 +419,21 @@
 			ui |= ((uint64_t)1 << (len - i - 1));
 		bv->cur_bit++;
 	}
-	read_index += len;
+	*read_index += len;
 	return ui;
 }
 
 /*! \brief write into the vector
  *  \param[in] bv The boolean vector to work on
- *  \param[in] write_index Where writing supposed to start in the vector
+ *  \param[in,out] write_index Where writing supposed to start in the vector
  *  \param[in] len How many bits to write
  *  \returns next write index or negative value on error
  */
-int bitvec_write_field(struct bitvec *bv, unsigned int write_index, uint64_t val, unsigned int len)
+int bitvec_write_field(struct bitvec *bv, unsigned int *write_index, uint64_t val, unsigned int len)
 {
 	unsigned int i;
 	int rc;
-	bv->cur_bit = write_index;
+	bv->cur_bit = *write_index;
 	for (i = 0; i < len; i++) {
 		int bit = 0;
 		if (val & ((uint64_t)1 << (len - i - 1)))
@@ -442,7 +442,7 @@
 		if (rc)
 			return rc;
 	}
-	write_index += len;
+	*write_index += len;
 	return 0;
 }
 
diff --git a/tests/bitvec/bitvec_test.c b/tests/bitvec/bitvec_test.c
index 624e334..789df75 100644
--- a/tests/bitvec/bitvec_test.c
+++ b/tests/bitvec/bitvec_test.c
@@ -55,8 +55,24 @@
 	printf("=== end %s ===\n", __func__);
 }
 
+static void test_unhex(const char *hex)
+{
+	struct bitvec b;
+	uint8_t d[64] = {0};
+	b.data = d;
+	b.data_len = sizeof(d);
+	b.cur_bit = 0;
+	printf("%d -=>\n", bitvec_unhex(&b, hex));
+	printf("%s\n%s\n", osmo_hexdump_nospc(d, 64), osmo_hexdump_nospc((const unsigned char *)hex, 23));
+}
+
 int main(int argc, char **argv)
 {
 	test_byte_ops();
+	test_unhex("48282407a6a074227201000b2b2b2b2b2b2b2b2b2b2b2b");
+	test_unhex("47240c00400000000000000079eb2ac9402b2b2b2b2b2b");
+	test_unhex("47283c367513ba333004242b2b2b2b2b2b2b2b2b2b2b2b");
+	test_unhex("DEADFACE000000000000000000000000000000BEEFFEED");
+	test_unhex("FFFFFAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAABBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB");
 	return 0;
 }
diff --git a/tests/bitvec/bitvec_test.ok b/tests/bitvec/bitvec_test.ok
index 1f329af..8d944bc 100644
--- a/tests/bitvec/bitvec_test.ok
+++ b/tests/bitvec/bitvec_test.ok
@@ -1,2 +1,17 @@
 === start test_byte_ops ===
 === end test_byte_ops ===
+1 -=>
+48282407a6a074227201000b2b2b2b2b2b2b2b2b2b2b2b0000000000000000000000000000000000000000000000000000000000000000000000000000000000
+48282407a6a074227201000b2b2b2b2b2b2b2b2b2b2b2b0000000000000000000000000000000000000000000000000000000000000000000000000000000000
+1 -=>
+47240c00400000000000000079eb2ac9402b2b2b2b2b2b0000000000000000000000000000000000000000000000000000000000000000000000000000000000
+47240c00400000000000000079eb2ac9402b2b2b2b2b2b0000000000000000000000000000000000000000000000000000000000000000000000000000000000
+1 -=>
+47283c367513ba333004242b2b2b2b2b2b2b2b2b2b2b2b0000000000000000000000000000000000000000000000000000000000000000000000000000000000
+47283c367513ba333004242b2b2b2b2b2b2b2b2b2b2b2b0000000000000000000000000000000000000000000000000000000000000000000000000000000000
+1 -=>
+deadface000000000000000000000000000000beeffeed0000000000000000000000000000000000000000000000000000000000000000000000000000000000
+deadface000000000000000000000000000000beeffeed0000000000000000000000000000000000000000000000000000000000000000000000000000000000
+0 -=>
+fffffaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+fffffaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa