diff --git a/Makefile b/Makefile
index 15247cf1f6..ea978be052 100644
--- a/Makefile
+++ b/Makefile
@@ -53,7 +53,7 @@ OBJS   = $(SRCS:.c=.o)
 TESTLIBS = $(shell pkg-config --libs check) -lrt -lpthread -lm
 TESTSSLLIBS = -lcrypto
 
-all: tests test-openssl libtrezor-crypto.so test_speed tools
+all: tests test-openssl test_speed tools libtrezor-crypto.so
 
 %.o: %.c %.h options.h
 	$(CC) $(CFLAGS) -o $@ -c $<
diff --git a/bignum.c b/bignum.c
index b2a20f9747..c06bd53dad 100644
--- a/bignum.c
+++ b/bignum.c
@@ -960,6 +960,58 @@ void bn_divmod1000(bignum256 *a, uint32_t *r)
 	*r = rem;
 }
 
+// 2^256 has 78 digits in decimal (+ 1 for decimal point, + 1 for leading zero, + 1 for trailing zero)
+#define DIGITLEN (78 + 1 + 1 + 1)
+
+int bn_format(const bignum256 *amnt, const char *prefix, const char *suffix, int decimals, char *out, int outlen)
+{
+	// convert bignum to characters
+	bignum256 val;
+	memcpy(&val, amnt, sizeof(bignum256));
+	char digits[DIGITLEN];
+	memset(digits, '0', DIGITLEN);
+	int pos = 1; // keep one trailing zero
+	for (int i = 0; i < 78 / 3; i++) {
+		uint32_t limb;
+		bn_divmod1000(&val, &limb);
+		if (pos == decimals + 1) { digits[DIGITLEN - 1 - pos] = '.'; pos++; }
+		digits[DIGITLEN - 1 - pos] = '0' + (limb % 10); pos++;
+		if (pos == decimals + 1) { digits[DIGITLEN - 1 - pos] = '.'; pos++; }
+		digits[DIGITLEN - 1 - pos] = '0' + ((limb / 10) % 10); pos++;
+		if (pos == decimals + 1) { digits[DIGITLEN - 1 - pos] = '.'; pos++; }
+		digits[DIGITLEN - 1 - pos] = '0' + ((limb / 100) % 10); pos++;
+	}
+
+	// drop leading zeroes
+	int digitstart = 0;
+	while (digitstart < DIGITLEN - 1 && digits[digitstart] == '0' && digits[digitstart + 1] >= '0' && digits[digitstart + 1] <= '9') {
+		digitstart++;
+	}
+
+	// drop trailing zeroes
+	int digitend = DIGITLEN - 1;
+	while (digitend > 0 && digits[digitend] == '0' && digits[digitend - 1] >= '0' && digits[digitend - 1] <= '9') {
+		digitend--;
+	}
+
+	int digitslen = digitend - digitstart + 1;
+	int prefixlen = prefix != NULL ? strlen(prefix) : 0;
+	int suffixlen = suffix != NULL ? strlen(suffix) : 0;
+
+	// output buffer is too small
+	if (prefixlen + digitslen + suffixlen + 1 > outlen) {
+		return 0;
+	}
+
+	// copy result to output buffer
+	memcpy(out, prefix, prefixlen);
+	memcpy(out + prefixlen, digits + digitstart, digitslen);
+	memcpy(out + prefixlen + digitslen, suffix, suffixlen);
+	out[prefixlen + digitslen + suffixlen] = 0;
+
+	return prefixlen + digitslen + suffixlen;
+}
+
 #if USE_BN_PRINT
 void bn_print(const bignum256 *a)
 {
diff --git a/bignum.h b/bignum.h
index 83ae314ce9..8e23ab9760 100644
--- a/bignum.h
+++ b/bignum.h
@@ -145,6 +145,8 @@ void bn_divmod58(bignum256 *a, uint32_t *r);
 
 void bn_divmod1000(bignum256 *a, uint32_t *r);
 
+int bn_format(const bignum256 *amnt, const char *prefix, const char *suffix, int decimals, char *out, int outlen);
+
 #if USE_BN_PRINT
 void bn_print(const bignum256 *a);
 void bn_print_raw(const bignum256 *a);
diff --git a/tests.c b/tests.c
index f77752837b..4c9c6be218 100644
--- a/tests.c
+++ b/tests.c
@@ -353,6 +353,138 @@ START_TEST(test_bignum_is_less)
 }
 END_TEST
 
+START_TEST(test_bignum_format) {
+	bignum256 a;
+	char buf[128];
+	int r;
+
+	bn_read_be(fromhex("0000000000000000000000000000000000000000000000000000000000000000"), &a);
+	r = bn_format(&a, NULL, NULL, 0, buf, sizeof(buf));
+	ck_assert_int_eq(r, 3);
+	ck_assert_str_eq(buf, "0.0");
+
+	bn_read_be(fromhex("0000000000000000000000000000000000000000000000000000000000000000"), &a);
+	r = bn_format(&a, "", "", 0, buf, sizeof(buf));
+	ck_assert_int_eq(r, 3);
+	ck_assert_str_eq(buf, "0.0");
+
+	bn_read_be(fromhex("0000000000000000000000000000000000000000000000000000000000000000"), &a);
+	r = bn_format(&a, NULL, "SFFX", 0, buf, sizeof(buf));
+	ck_assert_int_eq(r, 3 + 4);
+	ck_assert_str_eq(buf, "0.0SFFX");
+
+	bn_read_be(fromhex("0000000000000000000000000000000000000000000000000000000000000000"), &a);
+	r = bn_format(&a, "PRFX", NULL, 0, buf, sizeof(buf));
+	ck_assert_int_eq(r, 4 + 3);
+	ck_assert_str_eq(buf, "PRFX0.0");
+
+	bn_read_be(fromhex("0000000000000000000000000000000000000000000000000000000000000000"), &a);
+	r = bn_format(&a, "PRFX", "SFFX", 0, buf, sizeof(buf));
+	ck_assert_int_eq(r, 4 + 3 + 4);
+	ck_assert_str_eq(buf, "PRFX0.0SFFX");
+
+	bn_read_be(fromhex("0000000000000000000000000000000000000000000000000000000000000000"), &a);
+	r = bn_format(&a, NULL, NULL, 18, buf, sizeof(buf));
+	ck_assert_int_eq(r, 3);
+	ck_assert_str_eq(buf, "0.0");
+
+	bn_read_be(fromhex("0000000000000000000000000000000000000000000000000000000000000001"), &a);
+	r = bn_format(&a, NULL, NULL, 0, buf, sizeof(buf));
+	ck_assert_int_eq(r, 3);
+	ck_assert_str_eq(buf, "1.0");
+
+	bn_read_be(fromhex("0000000000000000000000000000000000000000000000000000000000000002"), &a);
+	r = bn_format(&a, NULL, NULL, 0, buf, sizeof(buf));
+	ck_assert_int_eq(r, 3);
+	ck_assert_str_eq(buf, "2.0");
+
+	bn_read_be(fromhex("0000000000000000000000000000000000000000000000000000000000000005"), &a);
+	r = bn_format(&a, NULL, NULL, 0, buf, sizeof(buf));
+	ck_assert_int_eq(r, 3);
+	ck_assert_str_eq(buf, "5.0");
+
+	bn_read_be(fromhex("000000000000000000000000000000000000000000000000000000000000000a"), &a);
+	r = bn_format(&a, NULL, NULL, 0, buf, sizeof(buf));
+	ck_assert_int_eq(r, 4);
+	ck_assert_str_eq(buf, "10.0");
+
+	bn_read_be(fromhex("0000000000000000000000000000000000000000000000000000000000000014"), &a);
+	r = bn_format(&a, NULL, NULL, 0, buf, sizeof(buf));
+	ck_assert_int_eq(r, 4);
+	ck_assert_str_eq(buf, "20.0");
+
+	bn_read_be(fromhex("0000000000000000000000000000000000000000000000000000000000000032"), &a);
+	r = bn_format(&a, NULL, NULL, 0, buf, sizeof(buf));
+	ck_assert_int_eq(r, 4);
+	ck_assert_str_eq(buf, "50.0");
+
+	bn_read_be(fromhex("0000000000000000000000000000000000000000000000000000000000000064"), &a);
+	r = bn_format(&a, NULL, NULL, 0, buf, sizeof(buf));
+	ck_assert_int_eq(r, 5);
+	ck_assert_str_eq(buf, "100.0");
+
+	bn_read_be(fromhex("00000000000000000000000000000000000000000000000000000000000000c8"), &a);
+	r = bn_format(&a, NULL, NULL, 0, buf, sizeof(buf));
+	ck_assert_int_eq(r, 5);
+	ck_assert_str_eq(buf, "200.0");
+
+	bn_read_be(fromhex("00000000000000000000000000000000000000000000000000000000000001f4"), &a);
+	r = bn_format(&a, NULL, NULL, 0, buf, sizeof(buf));
+	ck_assert_int_eq(r, 5);
+	ck_assert_str_eq(buf, "500.0");
+
+	bn_read_be(fromhex("00000000000000000000000000000000000000000000000000000000000003e8"), &a);
+	r = bn_format(&a, NULL, NULL, 0, buf, sizeof(buf));
+	ck_assert_int_eq(r, 6);
+	ck_assert_str_eq(buf, "1000.0");
+
+	bn_read_be(fromhex("0000000000000000000000000000000000000000000000000000000000989680"), &a);
+	r = bn_format(&a, NULL, NULL, 7, buf, sizeof(buf));
+	ck_assert_int_eq(r, 3);
+	ck_assert_str_eq(buf, "1.0");
+
+	bn_read_be(fromhex("ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff"), &a);
+	r = bn_format(&a, NULL, NULL, 0, buf, sizeof(buf));
+	ck_assert_int_eq(r, 80);
+	ck_assert_str_eq(buf, "115792089237316195423570985008687907853269984665640564039457584007913129639935.0");
+
+	bn_read_be(fromhex("ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff"), &a);
+	r = bn_format(&a, NULL, NULL, 1, buf, sizeof(buf));
+	ck_assert_int_eq(r, 79);
+	ck_assert_str_eq(buf, "11579208923731619542357098500868790785326998466564056403945758400791312963993.5");
+
+	bn_read_be(fromhex("ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff"), &a);
+	r = bn_format(&a, NULL, NULL, 2, buf, sizeof(buf));
+	ck_assert_int_eq(r, 79);
+	ck_assert_str_eq(buf, "1157920892373161954235709850086879078532699846656405640394575840079131296399.35");
+
+	bn_read_be(fromhex("ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff"), &a);
+	r = bn_format(&a, NULL, NULL, 8, buf, sizeof(buf));
+	ck_assert_int_eq(r, 79);
+	ck_assert_str_eq(buf, "1157920892373161954235709850086879078532699846656405640394575840079131.29639935");
+
+	bn_read_be(fromhex("fffffffffffffffffffffffffffffffffffffffffffffffffffffffffe3bbb00"), &a);
+	r = bn_format(&a, NULL, NULL, 8, buf, sizeof(buf));
+	ck_assert_int_eq(r, 72);
+	ck_assert_str_eq(buf, "1157920892373161954235709850086879078532699846656405640394575840079131.0");
+
+	bn_read_be(fromhex("ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff"), &a);
+	r = bn_format(&a, NULL, NULL, 18, buf, sizeof(buf));
+	ck_assert_int_eq(r, 79);
+	ck_assert_str_eq(buf, "115792089237316195423570985008687907853269984665640564039457.584007913129639935");
+
+	bn_read_be(fromhex("fffffffffffffffffffffffffffffffffffffffffffffffff7e52fe5afe40000"), &a);
+	r = bn_format(&a, NULL, NULL, 18, buf, sizeof(buf));
+	ck_assert_int_eq(r, 62);
+	ck_assert_str_eq(buf, "115792089237316195423570985008687907853269984665640564039457.0");
+
+	bn_read_be(fromhex("ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff"), &a);
+	r = bn_format(&a, "quite a long prefix", "even longer suffix", 60, buf, sizeof(buf));
+	ck_assert_int_eq(r, 116);
+	ck_assert_str_eq(buf, "quite a long prefix115792089237316195.423570985008687907853269984665640564039457584007913129639935even longer suffix");
+}
+END_TEST
+
 // from https://github.com/bitcoin/bitcoin/blob/master/src/test/data/base58_keys_valid.json
 START_TEST(test_base58)
 {
@@ -2960,6 +3092,7 @@ Suite *test_suite(void)
 	tcase_add_test(tc, test_bignum_is_odd);
 	tcase_add_test(tc, test_bignum_bitcount);
 	tcase_add_test(tc, test_bignum_is_less);
+	tcase_add_test(tc, test_bignum_format);
 	suite_add_tcase(s, tc);
 
 	tc = tcase_create("base58");
@@ -3107,7 +3240,7 @@ Suite *test_suite(void)
 	tcase_add_test(tc, test_ethereum_pubkeyhash);
 	suite_add_tcase(s, tc);
 
-	tc = tcase_create("multibyte_addresse");
+	tc = tcase_create("multibyte_address");
 	tcase_add_test(tc, test_multibyte_address);
 	suite_add_tcase(s, tc);