diff --git a/core/net/mac/contikimac/contikimac.c b/core/net/mac/contikimac/contikimac.c
index 30a532511..1a99720fd 100644
--- a/core/net/mac/contikimac/contikimac.c
+++ b/core/net/mac/contikimac/contikimac.c
@@ -544,7 +544,9 @@ send_packet(mac_callback_t mac_callback, void *mac_callback_ptr,
   int strobes;
   uint8_t got_strobe_ack = 0;
   uint8_t is_broadcast = 0;
+#if WITH_PHASE_OPTIMIZATION
   uint8_t is_known_receiver = 0;
+#endif
   uint8_t collisions;
   int transmit_len;
   int ret;
@@ -1067,7 +1069,7 @@ turn_off(int keep_radio_on)
   }
 }
 /*---------------------------------------------------------------------------*/
-static unsigned short
+static clock_time_t
 duty_cycle(void)
 {
   return (1ul * CLOCK_SECOND * CYCLE_TIME) / RTIMER_ARCH_SECOND;
diff --git a/core/net/mac/cxmac/cxmac.c b/core/net/mac/cxmac/cxmac.c
index e07fde3d9..afafe8d99 100644
--- a/core/net/mac/cxmac/cxmac.c
+++ b/core/net/mac/cxmac/cxmac.c
@@ -918,7 +918,7 @@ turn_off(int keep_radio_on)
   }
 }
 /*---------------------------------------------------------------------------*/
-static unsigned short
+static clock_time_t
 channel_check_interval(void)
 {
   return (1ul * CLOCK_SECOND * DEFAULT_PERIOD) / RTIMER_ARCH_SECOND;
diff --git a/core/net/mac/nordc.c b/core/net/mac/nordc.c
index bb41335ff..5c94c0822 100644
--- a/core/net/mac/nordc.c
+++ b/core/net/mac/nordc.c
@@ -70,7 +70,7 @@ off(int keep_radio_on)
   return 0;
 }
 /*---------------------------------------------------------------------------*/
-static unsigned short
+static clock_time_t
 channel_check_interval(void)
 {
   return 0;
diff --git a/core/net/mac/nullrdc-noframer.c b/core/net/mac/nullrdc-noframer.c
index 562b5cbca..741861093 100644
--- a/core/net/mac/nullrdc-noframer.c
+++ b/core/net/mac/nullrdc-noframer.c
@@ -87,7 +87,7 @@ off(int keep_radio_on)
   }
 }
 /*---------------------------------------------------------------------------*/
-static unsigned short
+static clock_time_t
 channel_check_interval(void)
 {
   return 0;
diff --git a/core/net/mac/nullrdc.c b/core/net/mac/nullrdc.c
index 5cec23a3d..6675094d5 100644
--- a/core/net/mac/nullrdc.c
+++ b/core/net/mac/nullrdc.c
@@ -343,7 +343,7 @@ off(int keep_radio_on)
   }
 }
 /*---------------------------------------------------------------------------*/
-static unsigned short
+static clock_time_t
 channel_check_interval(void)
 {
   return 0;
diff --git a/core/net/mac/rdc.h b/core/net/mac/rdc.h
index 0818a9b40..827e6970a 100644
--- a/core/net/mac/rdc.h
+++ b/core/net/mac/rdc.h
@@ -86,7 +86,7 @@ struct rdc_driver {
   int (* off)(int keep_radio_on);
 
   /** Returns the channel check interval, expressed in clock_time_t ticks. */
-  unsigned short (* channel_check_interval)(void);
+  clock_time_t (* channel_check_interval)(void);
 };
 
 #endif /* RDC_H_ */
diff --git a/core/net/mac/sicslowmac/sicslowmac.c b/core/net/mac/sicslowmac/sicslowmac.c
index 09d77ae17..d5a62f1bc 100644
--- a/core/net/mac/sicslowmac/sicslowmac.c
+++ b/core/net/mac/sicslowmac/sicslowmac.c
@@ -251,7 +251,7 @@ init(void)
   NETSTACK_RADIO.on();
 }
 /*---------------------------------------------------------------------------*/
-static unsigned short
+static clock_time_t
 channel_check_interval(void)
 {
   return 0;
diff --git a/examples/cc2530dk/sniffer/stub-rdc.c b/examples/cc2530dk/sniffer/stub-rdc.c
index a4db0710d..3d7d212a0 100644
--- a/examples/cc2530dk/sniffer/stub-rdc.c
+++ b/examples/cc2530dk/sniffer/stub-rdc.c
@@ -76,7 +76,7 @@ off(int keep_radio_on)
   return keep_radio_on;
 }
 /*---------------------------------------------------------------------------*/
-static unsigned short
+static clock_time_t
 cca(void)
 {
   return 0;
diff --git a/examples/cc2538-common/sniffer/stub-rdc.c b/examples/cc2538-common/sniffer/stub-rdc.c
index a8c54de6a..ea15c3621 100644
--- a/examples/cc2538-common/sniffer/stub-rdc.c
+++ b/examples/cc2538-common/sniffer/stub-rdc.c
@@ -72,7 +72,7 @@ off(int keep_radio_on)
   return keep_radio_on;
 }
 /*---------------------------------------------------------------------------*/
-static unsigned short
+static clock_time_t
 cca(void)
 {
   return 0;
diff --git a/examples/ipv6/native-border-router/border-router-rdc.c b/examples/ipv6/native-border-router/border-router-rdc.c
index 4aae30e5e..0b0a0fd07 100644
--- a/examples/ipv6/native-border-router/border-router-rdc.c
+++ b/examples/ipv6/native-border-router/border-router-rdc.c
@@ -170,7 +170,7 @@ off(int keep_radio_on)
   return 1;
 }
 /*---------------------------------------------------------------------------*/
-static unsigned short
+static clock_time_t
 channel_check_interval(void)
 {
   return 0;
diff --git a/examples/osd/native-border-router/border-router-rdc.c b/examples/osd/native-border-router/border-router-rdc.c
index 4aae30e5e..0b0a0fd07 100644
--- a/examples/osd/native-border-router/border-router-rdc.c
+++ b/examples/osd/native-border-router/border-router-rdc.c
@@ -170,7 +170,7 @@ off(int keep_radio_on)
   return 1;
 }
 /*---------------------------------------------------------------------------*/
-static unsigned short
+static clock_time_t
 channel_check_interval(void)
 {
   return 0;