diff --git a/src/hci.c b/src/hci.c
index 6dc7216e4..2ff3ef620 100644
--- a/src/hci.c
+++ b/src/hci.c
@@ -108,7 +108,7 @@ static hci_connection_t * create_connection_for_addr(bd_addr_t addr){
     if (!conn) return NULL;
     BD_ADDR_COPY(conn->address, addr);
     conn->con_handle = 0xffff;
-    conn->authentication_flags = 0;
+    conn->authentication_flags = AUTH_FLAGS_NONE;
 #ifdef HAVE_TIME
     linked_item_set_user(&conn->timeout.item, conn);
     conn->timeout.process = hci_connection_timeout_handler;
diff --git a/src/hci.h b/src/hci.h
index c5dafe170..838ff377a 100644
--- a/src/hci.h
+++ b/src/hci.h
@@ -153,6 +153,7 @@ extern "C" {
  * Connection State 
  */
 typedef enum {
+    AUTH_FLAGS_NONE                = 0x00,
     RECV_LINK_KEY_REQUEST          = 0x01,
     HANDLE_LINK_KEY_REQUEST        = 0x02,
     SENT_LINK_KEY_REPLY            = 0x04,
diff --git a/src/l2cap.c b/src/l2cap.c
index afd5b7ed9..7e27cdb5a 100644
--- a/src/l2cap.c
+++ b/src/l2cap.c
@@ -83,6 +83,7 @@ typedef enum {
 } L2CAP_STATE;
 
 typedef enum {
+    STATE_VAR_NONE          = 0,
     STATE_VAR_RCVD_CONF_REQ = 1 << 0,
     STATE_VAR_RCVD_CONF_RSP = 1 << 1,
     STATE_VAR_SEND_CONF_REQ = 1 << 2,
@@ -501,7 +502,7 @@ void l2cap_create_channel_internal(void * connection, btstack_packet_handler_t p
     
     // set initial state
     chan->state = L2CAP_STATE_WILL_SEND_CREATE_CONNECTION;
-    chan->state_var = 0;
+    chan->state_var = STATE_VAR_NONE;
     chan->remote_sig_id = L2CAP_SIG_ID_INVALID;
     chan->local_sig_id = L2CAP_SIG_ID_INVALID;
     
@@ -697,7 +698,7 @@ static void l2cap_handle_connection_request(hci_con_handle_t handle, uint8_t sig
     
     // set initial state
     channel->state = L2CAP_STATE_WAIT_CLIENT_ACCEPT_OR_REJECT;
-    channel->state_var = 0;
+    channel->state_var = STATE_VAR_NONE;
     
     // add to connections list
     linked_list_add(&l2cap_channels, (linked_item_t *) channel);
diff --git a/src/rfcomm.c b/src/rfcomm.c
index 871146729..46325dca0 100644
--- a/src/rfcomm.c
+++ b/src/rfcomm.c
@@ -118,6 +118,7 @@ typedef enum {
 } RFCOMM_CHANNEL_STATE;
 
 typedef enum {
+    STATE_VAR_NONE            = 0,
     STATE_VAR_CLIENT_ACCEPTED = 1 << 0,
     STATE_VAR_RCVD_PN         = 1 << 1,
     STATE_VAR_RCVD_RPN        = 1 << 2,
@@ -443,7 +444,7 @@ static void rfcomm_channel_initialize(rfcomm_channel_t *channel, rfcomm_multiple
     bzero(channel, sizeof(rfcomm_channel_t));
     
     channel->state             = RFCOMM_CHANNEL_CLOSED;
-    channel->state_var         = 0;
+    channel->state_var         = STATE_VAR_NONE;
     
     channel->multiplexer      = multiplexer;
     channel->service          = service;
diff --git a/src/sdp.c b/src/sdp.c
index f96ae2929..e6fcd1ed8 100644
--- a/src/sdp.c
+++ b/src/sdp.c
@@ -582,7 +582,7 @@ static void sdp_packet_handler(uint8_t packet_type, uint16_t channel, uint8_t *p
 	switch (packet_type) {
 			
 		case L2CAP_DATA_PACKET:
-            pdu_id = packet[0];
+            pdu_id = (SDP_PDU_ID_t) packet[0];
             transaction_id = READ_NET_16(packet, 1);
             param_len = READ_NET_16(packet, 3);
             remote_mtu = l2cap_get_remote_mtu_for_local_cid(channel);
diff --git a/src/sdp_util.c b/src/sdp_util.c
index bfcb60de3..9c91d0b66 100644
--- a/src/sdp_util.c
+++ b/src/sdp_util.c
@@ -54,11 +54,11 @@ void sdp_normalize_uuid(uint8_t *uuid, uint32_t shortUUID){
 
 // MARK: DataElement getter
 de_size_t de_get_size_type(uint8_t *header){
-    return header[0] & 7;
+    return (de_size_t) (header[0] & 7);
 }
 
 de_type_t de_get_element_type(uint8_t *header){
-    return header[0] >> 3;
+    return (de_type_t) (header[0] >> 3);
 }
 
 int de_get_header_size(uint8_t * header){