diff --git a/isisd/isis_tlvs.c b/isisd/isis_tlvs.c
index b7389947b7..55b0a362f6 100644
--- a/isisd/isis_tlvs.c
+++ b/isisd/isis_tlvs.c
@@ -1312,7 +1312,7 @@ static int unpack_tlv_dynamic_hostname(enum isis_tlv_context context,
 	bool sane = true;
 	for (uint8_t i = 0; i < tlv_len; i++) {
 		if ((unsigned char)tlvs->hostname[i] > 127
-		    || !isprint(tlvs->hostname[i])) {
+		    || !isprint((int)tlvs->hostname[i])) {
 			sane = false;
 			tlvs->hostname[i] = '?';
 		}
diff --git a/lib/command.c b/lib/command.c
index 7b9b417839..d17f2c3d48 100644
--- a/lib/command.c
+++ b/lib/command.c
@@ -1862,7 +1862,7 @@ DEFUN (config_password,
 		return CMD_SUCCESS;
 	}
 
-	if (!isalnum(argv[idx_8]->arg[0])) {
+	if (!isalnum((int)argv[idx_8]->arg[0])) {
 		vty_out(vty,
 			"Please specify string starting with alphanumeric\n");
 		return CMD_WARNING_CONFIG_FAILED;
@@ -1914,7 +1914,7 @@ DEFUN (config_enable_password,
 		}
 	}
 
-	if (!isalnum(argv[idx_8]->arg[0])) {
+	if (!isalnum((int)argv[idx_8]->arg[0])) {
 		vty_out(vty,
 			"Please specify string starting with alphanumeric\n");
 		return CMD_WARNING_CONFIG_FAILED;
diff --git a/lib/command_graph.c b/lib/command_graph.c
index fce11a70cc..f00b126536 100644
--- a/lib/command_graph.c
+++ b/lib/command_graph.c
@@ -97,7 +97,7 @@ void cmd_token_varname_set(struct cmd_token *token, const char *varname)
 			token->varname[i] = '_';
 			break;
 		default:
-			token->varname[i] = tolower(varname[i]);
+			token->varname[i] = tolower((int)varname[i]);
 		}
 	token->varname[len] = '\0';
 }
diff --git a/lib/ptm_lib.c b/lib/ptm_lib.c
index dbfd2dc9f8..fea5a8cc40 100644
--- a/lib/ptm_lib.c
+++ b/lib/ptm_lib.c
@@ -120,7 +120,7 @@ static int _ptm_lib_decode_header(csv_t *csv, int *msglen, int *version,
 	}
 	/* remove leading spaces */
 	for (i = j = 0; i < csv_field_len(fld); i++) {
-		if (!isspace(hdr[i])) {
+		if (!isspace((int)hdr[i])) {
 			client_name[j] = hdr[i];
 			j++;
 		}
diff --git a/tools/start-stop-daemon.c b/tools/start-stop-daemon.c
index 8dc16f4209..6bf55b7740 100644
--- a/tools/start-stop-daemon.c
+++ b/tools/start-stop-daemon.c
@@ -396,7 +396,7 @@ static void parse_schedule_item(const char *string, struct schedule_item *item)
 
 	if (!strcmp(string, "forever")) {
 		item->type = sched_forever;
-	} else if (isdigit(string[0])) {
+	} else if (isdigit((int)string[0])) {
 		item->type = sched_timeout;
 		if (parse_integer(string, &item->value) != 0)
 			badusage("invalid timeout value in schedule");
diff --git a/vtysh/vtysh.c b/vtysh/vtysh.c
index 097f39fcf0..94c4ba4330 100644
--- a/vtysh/vtysh.c
+++ b/vtysh/vtysh.c
@@ -504,11 +504,11 @@ static char *trim(char *s)
 		return s;
 
 	end = s + size - 1;
-	while (end >= s && isspace(*end))
+	while (end >= s && isspace((int)*end))
 		end--;
 	*(end + 1) = '\0';
 
-	while (*s && isspace(*s))
+	while (*s && isspace((int)*s))
 		s++;
 
 	return s;