diff --git a/core/net/ip/resolv.c b/core/net/ip/resolv.c
index 58bda004d..edf2a4815 100644
--- a/core/net/ip/resolv.c
+++ b/core/net/ip/resolv.c
@@ -394,7 +394,7 @@ dns_name_isequal(const unsigned char *queryptr, const char *name,
         return 0;
       }
 
-      if(tolower(*name++) != tolower(*queryptr++)) {
+      if(tolower((unsigned int)*name++) != tolower((unsigned int)*queryptr++)) {
         return 0;
       }
     }
diff --git a/core/net/mac/contikimac/contikimac.c b/core/net/mac/contikimac/contikimac.c
index 7aea60928..b7083e83d 100644
--- a/core/net/mac/contikimac/contikimac.c
+++ b/core/net/mac/contikimac/contikimac.c
@@ -488,7 +488,9 @@ send_packet(mac_callback_t mac_callback, void *mac_callback_ptr,
             int is_receiver_awake)
 {
   rtimer_clock_t t0;
+#if WITH_PHASE_OPTIMIZATION
   rtimer_clock_t encounter_time = 0;
+#endif
   int strobes;
   uint8_t got_strobe_ack = 0;
   int len;
@@ -660,7 +662,9 @@ send_packet(mac_callback_t mac_callback, void *mac_callback_ptr,
 
     {
       rtimer_clock_t wt;
+#if WITH_PHASE_OPTIMIZATION
       rtimer_clock_t txtime = RTIMER_NOW();
+#endif
 #if RDC_CONF_HARDWARE_ACK
       int ret = NETSTACK_RADIO.transmit(transmit_len);
 #else
@@ -673,7 +677,9 @@ send_packet(mac_callback_t mac_callback, void *mac_callback_ptr,
       if(ret == RADIO_TX_OK) {
         if(!is_broadcast) {
           got_strobe_ack = 1;
+#if WITH_PHASE_OPTIMIZATION
           encounter_time = txtime;
+#endif
           break;
         }
       } else if (ret == RADIO_TX_NOACK) {
@@ -698,7 +704,9 @@ send_packet(mac_callback_t mac_callback, void *mac_callback_ptr,
         len = NETSTACK_RADIO.read(ackbuf, ACK_LEN);
         if(len == ACK_LEN && seqno == ackbuf[ACK_LEN - 1]) {
           got_strobe_ack = 1;
+#if WITH_PHASE_OPTIMIZATION
           encounter_time = txtime;
+#endif
           break;
         } else {
           PRINTF("contikimac: collisions while sending\n");
diff --git a/core/net/rime/collect-neighbor.c b/core/net/rime/collect-neighbor.c
index dae9289ea..b033d3e05 100644
--- a/core/net/rime/collect-neighbor.c
+++ b/core/net/rime/collect-neighbor.c
@@ -254,13 +254,11 @@ collect_neighbor_list_remove(struct collect_neighbor_list *neighbors_list,
 struct collect_neighbor *
 collect_neighbor_list_best(struct collect_neighbor_list *neighbors_list)
 {
-  int found;
   struct collect_neighbor *n, *best;
   uint16_t rtmetric;
 
   rtmetric = RTMETRIC_MAX;
   best = NULL;
-  found = 0;
 
   if(neighbors_list == NULL) {
     return NULL;
diff --git a/core/net/rime/collect.c b/core/net/rime/collect.c
index 325996246..cdd2557c3 100644
--- a/core/net/rime/collect.c
+++ b/core/net/rime/collect.c
@@ -950,14 +950,18 @@ node_packet_received(struct unicast_conn *c, const linkaddr_t *from)
   if(packetbuf_attr(PACKETBUF_ATTR_PACKET_TYPE) ==
      PACKETBUF_ATTR_PACKET_TYPE_DATA) {
     linkaddr_t ack_to;
+#if DEBUG
     uint8_t packet_seqno;
+#endif
 
     stats.datarecv++;
 
     /* Remember to whom we should send the ACK, since we reuse the
        packet buffer and its attributes when sending the ACK. */
     linkaddr_copy(&ack_to, packetbuf_addr(PACKETBUF_ADDR_SENDER));
+#if DEBUG
     packet_seqno = packetbuf_attr(PACKETBUF_ATTR_PACKET_ID);
+#endif
 
     /* If the queue is more than half filled, we add the CONGESTED
        flag to our outgoing acks. */
diff --git a/cpu/cc2538/usb/usb-arch.c b/cpu/cc2538/usb/usb-arch.c
index c209d7778..ed771ce83 100644
--- a/cpu/cc2538/usb/usb-arch.c
+++ b/cpu/cc2538/usb/usb-arch.c
@@ -872,7 +872,7 @@ fill_buffers(usb_buffer *buffer, uint8_t hw_ep, unsigned int len,
 static uint8_t
 ep0_get_setup_pkt(void)
 {
-  uint8_t res;
+  uint8_t res = 0;
   usb_buffer *buffer =
     skip_buffers_until(usb_endpoints[0].buffer, USB_BUFFER_SETUP,
                        USB_BUFFER_SETUP, &res);
@@ -916,8 +916,6 @@ ep0_get_data_pkt(void)
   }
 
   if(buffer->flags & (USB_BUFFER_SETUP | USB_BUFFER_IN)) {
-    uint8_t temp;
-
     buffer->flags |= USB_BUFFER_FAILED;
     buffer->flags &= ~USB_BUFFER_SUBMITTED;
     if(buffer->flags & USB_BUFFER_NOTIFY) {
@@ -925,7 +923,7 @@ ep0_get_data_pkt(void)
     }
     /* Flush the fifo */
     while(len--) {
-      temp = REG(USB_F0);
+      REG(USB_F0);
     }
     usb_endpoints[0].buffer = buffer->next;
     /* Force data stage end */