diff --git a/include/osmocom/gsm/gsm_utils.h b/include/osmocom/gsm/gsm_utils.h
index 38a3f6e08..de6343487 100644
--- a/include/osmocom/gsm/gsm_utils.h
+++ b/include/osmocom/gsm/gsm_utils.h
@@ -115,8 +115,7 @@ int gsm_septet_encode(uint8_t *result, const char *data);
 uint8_t gsm_get_octet_len(const uint8_t sept_len);
 int gsm_7bit_decode_n_hdr(char *decoded, size_t n, const uint8_t *user_data, uint8_t length, uint8_t ud_hdr_ind);
 
-unsigned int ms_class_gmsk_dbm(enum gsm_band band, int ms_class);
-
+int ms_class_gmsk_dbm(enum gsm_band band, int ms_class);
 int ms_pwr_ctl_lvl(enum gsm_band band, unsigned int dbm);
 int ms_pwr_dbm(enum gsm_band band, uint8_t lvl);
 
diff --git a/src/gsm/gsm_utils.c b/src/gsm/gsm_utils.c
index 365920fa5..ae77a9dca 100644
--- a/src/gsm/gsm_utils.c
+++ b/src/gsm/gsm_utils.c
@@ -501,8 +501,8 @@ size_t gsm0858_rsl_ul_meas_enc(struct gsm_meas_rep_unidir *mru, bool dtxd_used,
 /*! Convert power class to dBm according to GSM TS 05.05
  *  \param[in] band GSM frequency band
  *  \param[in] class GSM power class
- *  \returns maximum transmit power of power class in dBm */
-unsigned int ms_class_gmsk_dbm(enum gsm_band band, int class)
+ *  \returns maximum transmit power of power class in dBm, negative on error */
+int ms_class_gmsk_dbm(enum gsm_band band, int class)
 {
 	switch (band) {
 	case GSM_BAND_450:
diff --git a/tests/gsm0408/gsm0408_test.c b/tests/gsm0408/gsm0408_test.c
index 2488024a7..96178237c 100644
--- a/tests/gsm0408/gsm0408_test.c
+++ b/tests/gsm0408/gsm0408_test.c
@@ -1136,6 +1136,7 @@ static void test_si_range_helpers()
 static void test_power_ctrl()
 {
 	int8_t rc8;
+	int rc;
 
 	rc8 = osmo_gsm48_rfpowercap2powerclass(GSM_BAND_850, 0x00);
 	VERIFY(rc8, ==, 1);
@@ -1153,6 +1154,25 @@ static void test_power_ctrl()
 	VERIFY(rc8, <, 0);
 	rc8 = osmo_gsm48_rfpowercap2powerclass(GSM_BAND_900, 0xf2);
 	VERIFY(rc8, <, 0);
+
+	rc = ms_class_gmsk_dbm(GSM_BAND_850, 0);
+	VERIFY(rc, <, 0);
+	rc = ms_class_gmsk_dbm(GSM_BAND_850, 1);
+	VERIFY(rc, ==, 43);
+	rc = ms_class_gmsk_dbm(GSM_BAND_900, 3);
+	VERIFY(rc, ==, 37);
+	rc = ms_class_gmsk_dbm(GSM_BAND_1800, 2);
+	VERIFY(rc, ==, 24);
+	rc = ms_class_gmsk_dbm(GSM_BAND_1800, 3);
+	VERIFY(rc, ==, 36);
+	rc = ms_class_gmsk_dbm(GSM_BAND_1900, 3);
+	VERIFY(rc, ==, 33);
+	rc = ms_class_gmsk_dbm(GSM_BAND_1900, 4);
+	VERIFY(rc, <, 0);
+	rc = ms_class_gmsk_dbm(GSM_BAND_900, 5);
+	VERIFY(rc, ==, 29);
+	rc = ms_class_gmsk_dbm(GSM_BAND_900, 6);
+	VERIFY(rc, <, 0);
 }
 
 int main(int argc, char **argv)