diff --git a/apps/mosquitto_ctrl/ctrl_shell.c b/apps/mosquitto_ctrl/ctrl_shell.c
index 1cf30f5b..c3315d58 100644
--- a/apps/mosquitto_ctrl/ctrl_shell.c
+++ b/apps/mosquitto_ctrl/ctrl_shell.c
@@ -21,7 +21,6 @@ Contributors:
 #include <arpa/inet.h>
 #include <ctype.h>
 #include <errno.h>
-#include <editline/readline.h>
 #include <fcntl.h>
 #include <pthread.h>
 #include <signal.h>
@@ -131,7 +130,7 @@ static void term_set_canon(bool canon)
 void ctrl_shell_rtrim(char *buf)
 {
 	size_t slen = strlen(buf);
-	while(slen > 0 && isspace(buf[slen-1])){
+	while(slen > 0 && isspace((unsigned char)buf[slen-1])){
 		buf[slen-1] = '\0';
 		slen = strlen(buf);
 	}
diff --git a/apps/mosquitto_ctrl/ctrl_shell.h b/apps/mosquitto_ctrl/ctrl_shell.h
index 0acb5ff1..ee1e6dd1 100644
--- a/apps/mosquitto_ctrl/ctrl_shell.h
+++ b/apps/mosquitto_ctrl/ctrl_shell.h
@@ -24,6 +24,7 @@ extern "C" {
 
 #include <cjson/cJSON.h>
 #include <stdbool.h>
+#include <stdio.h>
 
 extern const char *ANSI_URL;
 extern const char *ANSI_MODULE;
diff --git a/apps/mosquitto_ctrl/ctrl_shell_dynsec.c b/apps/mosquitto_ctrl/ctrl_shell_dynsec.c
index 200cfe65..d15b6e8b 100644
--- a/apps/mosquitto_ctrl/ctrl_shell_dynsec.c
+++ b/apps/mosquitto_ctrl/ctrl_shell_dynsec.c
@@ -795,7 +795,7 @@ static void print_details(cJSON *j_data)
 	int64_t groupcount;
 	int64_t rolecount;
 	int64_t changeindex;
-	int align = strlen("Change index: ");
+	int align = (int)strlen("Change index: ");
 	json_get_int64(j_data, "clientCount", &clientcount, true, 0);
 	json_get_int64(j_data, "groupCount", &groupcount, true, 0);
 	json_get_int64(j_data, "roleCount", &rolecount, true, 0);
diff --git a/apps/mosquitto_ctrl/dynsec.c b/apps/mosquitto_ctrl/dynsec.c
index fdb6c6ce..b6ee50b2 100644
--- a/apps/mosquitto_ctrl/dynsec.c
+++ b/apps/mosquitto_ctrl/dynsec.c
@@ -184,7 +184,7 @@ static void print_json_array(cJSON *j_list, int slen, const char *label, const c
 static void print_client(cJSON *j_response)
 {
 	cJSON *j_data, *j_client, *jtmp;
-	const int label_width = strlen("Connections:");
+	const int label_width = (int)strlen("Connections:");
 
 	j_data = cJSON_GetObjectItem(j_response, "data");
 	if(j_data == NULL || !cJSON_IsObject(j_data)){
@@ -226,7 +226,7 @@ static void print_client(cJSON *j_response)
 static void print_group(cJSON *j_response)
 {
 	cJSON *j_data, *j_group;
-	int label_width = strlen("Groupname:");
+	int label_width = (int)strlen("Groupname:");
 	const char *groupname;
 
 	j_data = cJSON_GetObjectItem(j_response, "data");
diff --git a/apps/mosquitto_passwd/mosquitto_passwd.c b/apps/mosquitto_passwd/mosquitto_passwd.c
index f93a7ff1..f7d21d1a 100644
--- a/apps/mosquitto_passwd/mosquitto_passwd.c
+++ b/apps/mosquitto_passwd/mosquitto_passwd.c
@@ -413,7 +413,7 @@ static bool is_username_valid(const char *username)
 			return false;
 		}
 		for(i=0; i<slen; i++){
-			if(iscntrl(username[i])){
+			if(iscntrl((unsigned char)username[i])){
 				fprintf(stderr, "Error: Username must not contain control characters.\n");
 				return false;
 			}
diff --git a/lib/packet_mosq.c b/lib/packet_mosq.c
index 27616ac7..79ef165d 100644
--- a/lib/packet_mosq.c
+++ b/lib/packet_mosq.c
@@ -48,7 +48,7 @@ Contributors:
 
 int packet__alloc(struct mosquitto__packet **packet, uint8_t command, uint32_t remaining_length)
 {
-	uint8_t remaining_bytes[5], byte;
+	uint8_t remaining_bytes[5] = {0}, byte;
 	int8_t remaining_count;
 	uint32_t packet_length;
 	uint32_t remaining_length_stored;
diff --git a/libcommon/file_common.c b/libcommon/file_common.c
index 4895ad41..69b22b05 100644
--- a/libcommon/file_common.c
+++ b/libcommon/file_common.c
@@ -262,11 +262,11 @@ char *mosquitto_trimblanks(char *str)
 		return NULL;
 	}
 
-	while(isspace(str[0])){
+	while(isspace((unsigned char)str[0])){
 		str++;
 	}
 	endptr = &str[strlen(str)-1];
-	while(endptr > str && isspace(endptr[0])){
+	while(endptr > str && isspace((unsigned char)endptr[0])){
 		endptr[0] = '\0';
 		endptr--;
 	}
diff --git a/plugins/acl-file/acl_parse.c b/plugins/acl-file/acl_parse.c
index c9fd8a91..0547fd17 100644
--- a/plugins/acl-file/acl_parse.c
+++ b/plugins/acl-file/acl_parse.c
@@ -213,7 +213,7 @@ int acl_file__parse(struct acl_file_data *data)
 
 	while(mosquitto_fgets(&buf, &buflen, aclfptr)){
 		slen = strlen(buf);
-		while(slen > 0 && isspace(buf[slen-1])){
+		while(slen > 0 && isspace((unsigned char)buf[slen-1])){
 			buf[slen-1] = '\0';
 			slen = strlen(buf);
 		}
diff --git a/plugins/dynamic-security/config_init.c b/plugins/dynamic-security/config_init.c
index f3821719..e1867663 100644
--- a/plugins/dynamic-security/config_init.c
+++ b/plugins/dynamic-security/config_init.c
@@ -82,7 +82,7 @@ static int get_password_from_init_file(struct dynsec__data *data, char **pw)
 	fclose(fptr);
 
 	pos = (int)strlen(buf)-1;
-	while(pos >= 0 && isspace(buf[pos])){
+	while(pos >= 0 && isspace((unsigned char)buf[pos])){
 		buf[pos] = '\0';
 		pos--;
 	}
diff --git a/src/conf.c b/src/conf.c
index b680b479..74f281e8 100644
--- a/src/conf.c
+++ b/src/conf.c
@@ -3003,7 +3003,7 @@ static int config__check(struct mosquitto__config *config)
 		id_prefix_len = config->security_options.auto_id_prefix_len;
 	}else{
 		id_prefix = "auto-";
-		id_prefix_len = strlen("auto-");
+		id_prefix_len = (int)strlen("auto-");
 	}
 
 	/* Default to auto_id_prefix = 'auto-' if none set. */
diff --git a/src/conf_includedir.c b/src/conf_includedir.c
index feee6a57..96127708 100644
--- a/src/conf_includedir.c
+++ b/src/conf_includedir.c
@@ -59,7 +59,7 @@ static int scmp_p(const void *p1, const void *p2)
 
 	while(s1[0] && s2[0]){
 		/* Sort by case insensitive part first */
-		result = toupper(s1[0]) - toupper(s2[0]);
+		result = toupper((unsigned char)s1[0]) - toupper((unsigned char)s2[0]);
 		if(result == 0){
 			/* Case insensitive part matched, now distinguish between case */
 			result = s1[0] - s2[0];
diff --git a/src/control.c b/src/control.c
index 0c8812ad..a17828df 100644
--- a/src/control.c
+++ b/src/control.c
@@ -41,7 +41,7 @@ static void control__negative_reply(const char *clientid, const char *request_to
 	}
 	snprintf(response_topic, response_topic_len, "%s/response", request_topic);
 
-	mosquitto_broker_publish_copy(clientid, response_topic, strlen(payload), payload, 0, false, NULL);
+	mosquitto_broker_publish_copy(clientid, response_topic, (int)strlen(payload), payload, 0, false, NULL);
 	mosquitto_FREE(response_topic);
 }
 
diff --git a/src/listeners.c b/src/listeners.c
index c05d74ee..34c9a70c 100644
--- a/src/listeners.c
+++ b/src/listeners.c
@@ -172,7 +172,7 @@ static int listeners__add_local(const char *host, uint16_t port)
 		mosquitto_FREE(listeners[db.config->listener_count].security_options);
 		return MOSQ_ERR_NOMEM;
 	}
-	listeners[db.config->listener_count].security_options->auto_id_prefix_len = strlen("auto-");
+	listeners[db.config->listener_count].security_options->auto_id_prefix_len = (int)strlen("auto-");
 	listeners[db.config->listener_count].port = port;
 	listeners[db.config->listener_count].host = mosquitto_strdup(host);
 	if(listeners[db.config->listener_count].host == NULL){