diff --git a/cpu/cc2538/dev/cc2538-rf.c b/cpu/cc2538/dev/cc2538-rf.c
index dfbdfb699..17cbf7a1d 100644
--- a/cpu/cc2538/dev/cc2538-rf.c
+++ b/cpu/cc2538/dev/cc2538-rf.c
@@ -137,7 +137,6 @@ static int8_t rssi;
 static uint8_t crc_corr;
 
 void mac_timer_init(void);
-uint32_t get_sfd_timestamp(void);
 /*---------------------------------------------------------------------------*/
 static uint8_t rf_flags;
 static uint8_t rf_channel = CC2538_RF_CHANNEL;
@@ -380,6 +379,34 @@ set_auto_ack(uint8_t enable)
   }
 }
 /*---------------------------------------------------------------------------*/
+static uint32_t
+get_sfd_timestamp(void)
+{
+  uint64_t sfd, timer_val, buffer;
+
+  REG(RFCORE_SFR_MTMSEL) = (REG(RFCORE_SFR_MTMSEL) & ~RFCORE_SFR_MTMSEL_MTMSEL) | 0x00000000;
+  REG(RFCORE_SFR_MTCTRL) |= RFCORE_SFR_MTCTRL_LATCH_MODE;
+  timer_val = REG(RFCORE_SFR_MTM0) & RFCORE_SFR_MTM0_MTM0;
+  timer_val |= ((REG(RFCORE_SFR_MTM1) & RFCORE_SFR_MTM1_MTM1) << 8);
+  REG(RFCORE_SFR_MTMSEL) = (REG(RFCORE_SFR_MTMSEL) & ~RFCORE_SFR_MTMSEL_MTMOVFSEL) | 0x00000000;
+  timer_val |= ((REG(RFCORE_SFR_MTMOVF0) & RFCORE_SFR_MTMOVF0_MTMOVF0) << 16);
+  timer_val |= ((REG(RFCORE_SFR_MTMOVF1) & RFCORE_SFR_MTMOVF1_MTMOVF1) << 24);
+  buffer = REG(RFCORE_SFR_MTMOVF2) & RFCORE_SFR_MTMOVF2_MTMOVF2;
+  timer_val |= (buffer << 32);
+
+  REG(RFCORE_SFR_MTMSEL) = (REG(RFCORE_SFR_MTMSEL) & ~RFCORE_SFR_MTMSEL_MTMSEL) | 0x00000001;
+  REG(RFCORE_SFR_MTCTRL) |= RFCORE_SFR_MTCTRL_LATCH_MODE;
+  sfd = REG(RFCORE_SFR_MTM0) & RFCORE_SFR_MTM0_MTM0;
+  sfd |= ((REG(RFCORE_SFR_MTM1) & RFCORE_SFR_MTM1_MTM1) << 8);
+  REG(RFCORE_SFR_MTMSEL) = (REG(RFCORE_SFR_MTMSEL) & ~RFCORE_SFR_MTMSEL_MTMOVFSEL) | 0x00000010;
+  sfd |= ((REG(RFCORE_SFR_MTMOVF0) & RFCORE_SFR_MTMOVF0_MTMOVF0) << 16);
+  sfd |= ((REG(RFCORE_SFR_MTMOVF1) & RFCORE_SFR_MTMOVF1_MTMOVF1) << 24);
+  buffer = REG(RFCORE_SFR_MTMOVF2) & RFCORE_SFR_MTMOVF2_MTMOVF2;
+  sfd |= (buffer << 32);
+
+  return RTIMER_NOW() - RADIO_TO_RTIMER(timer_val - sfd);
+}
+/*---------------------------------------------------------------------------*/
 /* Netstack API radio driver functions */
 /*---------------------------------------------------------------------------*/
 static int
@@ -1128,33 +1155,6 @@ cc2538_rf_set_promiscous_mode(char p)
   set_frame_filtering(p);
 }
 /*---------------------------------------------------------------------------*/
-uint32_t get_sfd_timestamp(void)
-{
-  uint64_t sfd, timer_val, buffer;
-
-  REG(RFCORE_SFR_MTMSEL) = (REG(RFCORE_SFR_MTMSEL) & ~RFCORE_SFR_MTMSEL_MTMSEL) | 0x00000000;
-  REG(RFCORE_SFR_MTCTRL) |= RFCORE_SFR_MTCTRL_LATCH_MODE;
-  timer_val = REG(RFCORE_SFR_MTM0) & RFCORE_SFR_MTM0_MTM0;
-  timer_val |= ((REG(RFCORE_SFR_MTM1) & RFCORE_SFR_MTM1_MTM1) << 8);
-  REG(RFCORE_SFR_MTMSEL) = (REG(RFCORE_SFR_MTMSEL) & ~RFCORE_SFR_MTMSEL_MTMOVFSEL) | 0x00000000;
-  timer_val |= ((REG(RFCORE_SFR_MTMOVF0) & RFCORE_SFR_MTMOVF0_MTMOVF0) << 16);
-  timer_val |= ((REG(RFCORE_SFR_MTMOVF1) & RFCORE_SFR_MTMOVF1_MTMOVF1) << 24);
-  buffer = REG(RFCORE_SFR_MTMOVF2) & RFCORE_SFR_MTMOVF2_MTMOVF2;
-  timer_val |= (buffer << 32);
-
-  REG(RFCORE_SFR_MTMSEL) = (REG(RFCORE_SFR_MTMSEL) & ~RFCORE_SFR_MTMSEL_MTMSEL) | 0x00000001;
-  REG(RFCORE_SFR_MTCTRL) |= RFCORE_SFR_MTCTRL_LATCH_MODE;
-  sfd = REG(RFCORE_SFR_MTM0) & RFCORE_SFR_MTM0_MTM0;
-  sfd |= ((REG(RFCORE_SFR_MTM1) & RFCORE_SFR_MTM1_MTM1) << 8);
-  REG(RFCORE_SFR_MTMSEL) = (REG(RFCORE_SFR_MTMSEL) & ~RFCORE_SFR_MTMSEL_MTMOVFSEL) | 0x00000010;
-  sfd |= ((REG(RFCORE_SFR_MTMOVF0) & RFCORE_SFR_MTMOVF0_MTMOVF0) << 16);
-  sfd |= ((REG(RFCORE_SFR_MTMOVF1) & RFCORE_SFR_MTMOVF1_MTMOVF1) << 24);
-  buffer = REG(RFCORE_SFR_MTMOVF2) & RFCORE_SFR_MTMOVF2_MTMOVF2;
-  sfd |= (buffer << 32);
-
-  return (RTIMER_NOW() - RADIO_TO_RTIMER(timer_val - sfd));
-}
-/*---------------------------------------------------------------------------*/
 void mac_timer_init(void)
 {
   CLOCK_STABLE();