diff --git a/src/gsm/gsm48_ie.c b/src/gsm/gsm48_ie.c
index 863e63652..2a9a01003 100644
--- a/src/gsm/gsm48_ie.c
+++ b/src/gsm/gsm48_ie.c
@@ -659,6 +659,21 @@ int gsm48_encode_more(struct msgb *msg)
 	return 0;
 }
 
+static int32_t smod(int32_t n, int32_t m)
+{
+	int32_t res;
+
+	res = n % m;
+
+	if(res < 0)
+		res += m;
+
+	if(res == 0)
+		res = m;
+
+	return res;
+}
+
 /* decode "Cell Channel Description" (10.5.2.1b) and other frequency lists */
 int gsm48_decode_freq_list(struct gsm_sysinfo_freq *f, uint8_t *cd,
 			   uint8_t len, uint8_t mask, uint8_t frqt)
@@ -907,45 +922,45 @@ int gsm48_decode_freq_list(struct gsm_sysinfo_freq *f, uint8_t *cd,
 		if (w[1])
 			f[(w[0] + w[1]) % 1024].mask |= frqt;
 		if (w[2])
-			f[(w[0] + ((w[1] - 128 + w[2] - 1) % 255) + 1) % 1024].mask |= frqt;
+			f[(w[0] + smod(w[1] - 128 + w[2], 255)) % 1024].mask |= frqt;
 		if (w[3])
-			f[(w[0] + ((w[1]       + w[3] - 1) % 255) + 1) % 1024].mask |= frqt;
+			f[(w[0] + smod(w[1]       + w[3], 255)) % 1024].mask |= frqt;
 		if (w[4])
-			f[(w[0] + ((w[1] - 128 + ((w[2] - 64 + w[4] - 1) % 127)) % 255) + 1) % 1024].mask |= frqt;
+			f[(w[0] + smod(w[1] - 128 + smod(w[2] - 64 + w[4], 127), 255)) % 1024].mask |= frqt;
 		if (w[5])
-			f[(w[0] + ((w[1]       + ((w[3] - 64 + w[5] - 1) % 127)) % 255) + 1) % 1024].mask |= frqt;
+			f[(w[0] + smod(w[1]       + smod(w[3] - 64 + w[5], 127), 255)) % 1024].mask |= frqt;
 		if (w[6])
-			f[(w[0] + ((w[1] - 128 + ((w[2]      + w[6] - 1) % 127)) % 255) + 1) % 1024].mask |= frqt;
+			f[(w[0] + smod(w[1] - 128 + smod(w[2]      + w[6], 127), 255)) % 1024].mask |= frqt;
 		if (w[7])
-			f[(w[0] + ((w[1]       + ((w[3]      + w[7] - 1) % 127)) % 255) + 1) % 1024].mask |= frqt;
+			f[(w[0] + smod(w[1]       + smod(w[3]      + w[7], 127), 255)) % 1024].mask |= frqt;
 		if (w[8])
-			f[(w[0] + ((w[1] - 128 + ((w[2] - 64 + ((w[4] - 32 + w[8] - 1) % 63)) % 127)) % 255) + 1) % 1024].mask |= frqt;
+			f[(w[0] + smod(w[1] - 128 + smod(w[2] - 64 + smod(w[4] - 32 + w[8], 63), 127), 255)) % 1024].mask |= frqt;
 		if (w[9])
-			f[(w[0] + ((w[1]       + ((w[3] - 64 + ((w[5] - 32 + w[9] - 1) % 63)) % 127)) % 255) + 1) % 1024].mask |= frqt;
+			f[(w[0] + smod(w[1]       + smod(w[3] - 64 + smod(w[5] - 32 + w[9], 63), 127), 255)) % 1024].mask |= frqt;
 		if (w[10])
-			f[(w[0] + ((w[1] - 128 + ((w[2]      + ((w[6] - 32 + w[10] - 1) % 63)) % 127)) % 255) + 1) % 1024].mask |= frqt;
+			f[(w[0] + smod(w[1] - 128 + smod(w[2]      + smod(w[6] - 32 + w[10], 63), 127), 255)) % 1024].mask |= frqt;
 		if (w[11])
-			f[(w[0] + ((w[1]       + ((w[3]      + ((w[7] - 32 + w[11] - 1) % 63)) % 127)) % 255) + 1) % 1024].mask |= frqt;
+			f[(w[0] + smod(w[1]       + smod(w[3]      + smod(w[7] - 32 + w[11], 63), 127), 255)) % 1024].mask |= frqt;
 		if (w[12])
-			f[(w[0] + ((w[1] - 128 + ((w[2] - 64 + ((w[4]      + w[12] - 1) % 63)) % 127)) % 255) + 1) % 1024].mask |= frqt;
+			f[(w[0] + smod(w[1] - 128 + smod(w[2] - 64 + smod(w[4]      + w[12], 63), 127), 255)) % 1024].mask |= frqt;
 		if (w[13])
-			f[(w[0] + ((w[1]       + ((w[3] - 64 + ((w[5]      + w[13] - 1) % 63)) % 127)) % 255) + 1) % 1024].mask |= frqt;
+			f[(w[0] + smod(w[1]       + smod(w[3] - 64 + smod(w[5]      + w[13], 63), 127), 255)) % 1024].mask |= frqt;
 		if (w[14])
-			f[(w[0] + ((w[1] - 128 + ((w[2]      + ((w[6]      + w[14] - 1) % 63)) % 127)) % 255) + 1) % 1024].mask |= frqt;
+			f[(w[0] + smod(w[1] - 128 + smod(w[2]      + smod(w[6]      + w[14], 63), 127), 255)) % 1024].mask |= frqt;
 		if (w[15])
-			f[(w[0] + ((w[1]       + ((w[3]      + ((w[7]      + w[15] - 1) % 63)) % 127)) % 255) + 1) % 1024].mask |= frqt;
+			f[(w[0] + smod(w[1]       + smod(w[3]      + smod(w[7]      + w[15], 63), 127), 255)) % 1024].mask |= frqt;
 		if (w[16])
-			f[(w[0] + ((w[1] - 128 + ((w[2] - 64 + ((w[4] - 32 + ((w[8] - 16 + w[16] - 1) % 31)) % 63)) % 127)) % 255) + 1) % 1024].mask |= frqt;
+			f[(w[0] + smod(w[1] - 128 + smod(w[2] - 64 + smod(w[4] - 32 + smod(w[8] - 16 + w[16], 31), 63), 127), 255)) % 1024].mask |= frqt;
 		if (w[17])
-			f[(w[0] + ((w[1]       + ((w[3] - 64 + ((w[5] - 32 + ((w[9] - 16 + w[17] - 1) % 31)) % 63)) % 127)) % 255) + 1) % 1024].mask |= frqt;
+			f[(w[0] + smod(w[1]       + smod(w[3] - 64 + smod(w[5] - 32 + smod(w[9] - 16 + w[17], 31), 63), 127), 255)) % 1024].mask |= frqt;
 		if (w[18])
-			f[(w[0] + ((w[1] - 128 + ((w[2]      + ((w[6] - 32 + ((w[10] - 16 + w[18] - 1) % 31)) % 63)) % 127)) % 255) + 1) % 1024].mask |= frqt;
+			f[(w[0] + smod(w[1] - 128 + smod(w[2]      + smod(w[6] - 32 + smod(w[10] - 16 + w[18], 31), 63), 127), 255)) % 1024].mask |= frqt;
 		if (w[19])
-			f[(w[0] + ((w[1]       + ((w[3]      + ((w[7] - 32 + ((w[11] - 16 + w[19] - 1) % 31)) % 63)) % 127)) % 255) + 1) % 1024].mask |= frqt;
+			f[(w[0] + smod(w[1]       + smod(w[3]      + smod(w[7] - 32 + smod(w[11] - 16 + w[19], 31), 63), 127), 255)) % 1024].mask |= frqt;
 		if (w[20])
-			f[(w[0] + ((w[1] - 128 + ((w[2] - 64 + ((w[4]      + ((w[12] - 16 + w[20] - 1) % 31)) % 63)) % 127)) % 255) + 1) % 1024].mask |= frqt;
+			f[(w[0] + smod(w[1] - 128 + smod(w[2] - 64 + smod(w[4]      + smod(w[12] - 16 + w[20], 31), 63), 127), 255)) % 1024].mask |= frqt;
 		if (w[21])
-			f[(w[0] + ((w[1]       + ((w[3] - 64 + ((w[5]      + ((w[13] - 16 + w[21] - 1) % 31)) % 63)) % 127)) % 255) + 1) % 1024].mask |= frqt;
+			f[(w[0] + smod(w[1]       + smod(w[3] - 64 + smod(w[5]      + smod(w[13] - 16 + w[21], 31), 63), 127), 255)) % 1024].mask |= frqt;
 
 		return 0;
 	}