diff --git a/isup.c b/isup.c
index 6e1f091..1e9705c 100644
--- a/isup.c
+++ b/isup.c
@@ -169,7 +169,7 @@ static void isup_dump_buffer(struct ss7 
 	ss7_message(ss7, "]\n");
 }
 
-static void isup_get_number(char *dest, char *src, int srclen, int oddeven)
+static void isup_get_number(unsigned char *dest, unsigned char *src, int srclen, int oddeven)
 {
 	int i;
 	for (i = 0; i < ((srclen * 2) - oddeven); i++)
@@ -178,10 +178,10 @@ static void isup_get_number(char *dest, 
 	dest[i] = '\0'; 
 }
 
-static void isup_put_number(char *dest, char *src, int *len, int *oddeven)
+static void isup_put_number(unsigned char *dest, unsigned char *src, int *len, int *oddeven)
 {
 	int i = 0;
-	int numlen = strlen(src);
+	int numlen = strlen((char *) src);
 
 	if (numlen % 2) {
 		*oddeven = 1;
@@ -418,7 +418,7 @@ static FUNC_SEND(range_and_status_transm
 static FUNC_DUMP(calling_party_num_dump)
 {
 	int oddeven = (parm[0] >> 7) & 0x1;
-	char numbuf[64] = "";
+	unsigned char numbuf[64] = "";
 
 	ss7_message(ss7, "PARM: Calling Party Number\n");
 	ss7_message(ss7, "Odd/even: %x\n", (parm[0] >> 7) & 0x1);
@@ -514,14 +514,14 @@ struct isup_call * isup_new_call(struct 
 	return c;
 }
 
-void isup_init_call(struct isup_call *c, int cic, char *calledpartynum, char *callingpartynum)
+void isup_init_call(struct isup_call *c, int cic, unsigned char *calledpartynum, unsigned char *callingpartynum)
 {
 	c->cic = cic;
 	if (calledpartynum && calledpartynum[0])
-		snprintf(c->called_party_num, sizeof(c->called_party_num), "%s*", calledpartynum);
+		snprintf((char *) c->called_party_num, sizeof(c->called_party_num), "%s*", calledpartynum);
 
 	if (callingpartynum && callingpartynum[0])
-		strncpy(c->calling_party_num, callingpartynum, sizeof(c->calling_party_num));
+		strncpy((char *) c->calling_party_num, (char *) callingpartynum, sizeof(c->calling_party_num));
 
 }
 
@@ -876,8 +876,8 @@ int isup_receive(struct ss7 *ss7, struct
 			e->e = ISUP_EVENT_IAM;
 			e->iam.cic = c->cic;
 			e->iam.transcap = c->transcap;
-			strncpy(e->iam.called_party_num, c->called_party_num, sizeof(e->iam.called_party_num));
-			strncpy(e->iam.calling_party_num, c->calling_party_num, sizeof(e->iam.calling_party_num));
+			strncpy((char *) e->iam.called_party_num, (char *) c->called_party_num, sizeof(e->iam.called_party_num));
+			strncpy((char *) e->iam.calling_party_num, (char *) c->calling_party_num, sizeof(e->iam.calling_party_num));
 			e->iam.call = c;
 			return 0;
 		case ISUP_GRS:
diff --git a/isup.h b/isup.h
index 8845e1c..d6babf6 100644
--- a/isup.h
+++ b/isup.h
@@ -114,8 +114,8 @@ #define ISUP_MAX_NUM 64
 struct mtp2;
 
 struct isup_call {
-	char called_party_num[ISUP_MAX_NUM];
-	char calling_party_num[ISUP_MAX_NUM];
+	unsigned char called_party_num[ISUP_MAX_NUM];
+	unsigned char calling_party_num[ISUP_MAX_NUM];
 	int range;
 	int echocan;
 	int satellites;
diff --git a/libss7.h b/libss7.h
index 1d32621..c2d6eb8 100644
--- a/libss7.h
+++ b/libss7.h
@@ -156,5 +156,5 @@ int isup_gra(struct ss7 *ss7, int beginc
 
 int isup_grs(struct ss7 *ss7, int begincic, int endcic);
 
-void isup_init_call(struct isup_call *c, int cic, char *calledpartynum, char *callingpartynum);
+void isup_init_call(struct isup_call *c, int cic, unsigned char *calledpartynum, unsigned char *callingpartynum);
 #endif /* _LIBSS7_H */
diff --git a/mtp2.c b/mtp2.c
index 5133221..f5f2e05 100644
--- a/mtp2.c
+++ b/mtp2.c
@@ -146,7 +146,7 @@ static int mtp2_queue_su(struct mtp2 *li
 	return 0;
 }
 
-static void make_lssu(struct mtp2 *link, unsigned char *buf, int *size, int lssu_status)
+static void make_lssu(struct mtp2 *link, unsigned char *buf, unsigned int *size, int lssu_status)
 {
 	struct mtp_su_head *head;
 
@@ -174,7 +174,7 @@ static void make_lssu(struct mtp2 *link,
 	head->data[0] = lssu_status;
 }
 
-static void make_fisu(struct mtp2 *link, unsigned char *buf, int *size, int nack)
+static void make_fisu(struct mtp2 *link, unsigned char *buf, unsigned int *size, int nack)
 {
 	struct mtp_su_head *h;
 
@@ -203,7 +203,7 @@ int mtp2_transmit(struct mtp2 *link)
 	int res = 0;
 	unsigned char *h;
 	unsigned char buf[64];
-	int size;
+	unsigned int size;
 	struct ss7_msg *m = NULL;
 
 	if (link->tx_q)
diff --git a/mtp3.c b/mtp3.c
index 07b3cfc..b951eec 100644
--- a/mtp3.c
+++ b/mtp3.c
@@ -145,7 +145,7 @@ static void std_test_send(struct mtp2 *l
 	struct routing_label rl;
 	struct ss7 *ss7 = link->master;
 	int rllen = 0;
-	unsigned char testlen = strlen(testmessage);
+	unsigned char testlen = strlen((char *) testmessage);
 
 	m = ss7_msg_new();
 	if (!m) {
diff --git a/ss7.c b/ss7.c
index 47f904c..76e50fe 100644
--- a/ss7.c
+++ b/ss7.c
@@ -269,7 +269,7 @@ int ss7_write(struct ss7 *ss7, int fd)
 
 int ss7_read(struct ss7 *ss7, int fd)
 {
-	char buf[1024];
+	unsigned char buf[1024];
 	int res;
 	int winner = -1;
 	int i;