diff --git a/platform/cc2530dk/contiki-conf.h b/platform/cc2530dk/contiki-conf.h
index 1a3d16fb3..620ae2a17 100644
--- a/platform/cc2530dk/contiki-conf.h
+++ b/platform/cc2530dk/contiki-conf.h
@@ -62,6 +62,8 @@
 #define USB_SERIAL_CONF_BUFFERED 1
 #endif
 
+#define SLIP_RADIO_CONF_NO_PUTCHAR 1
+
 #if defined (UIP_FALLBACK_INTERFACE) || defined (CMD_CONF_OUTPUT)
 #define SLIP_ARCH_CONF_ENABLE      1
 #endif
diff --git a/platform/sensinode/contiki-conf.h b/platform/sensinode/contiki-conf.h
index 56f6cb3ed..19a815c07 100644
--- a/platform/sensinode/contiki-conf.h
+++ b/platform/sensinode/contiki-conf.h
@@ -62,6 +62,8 @@
 #define UART_ONE_CONF_HIGH_SPEED 0
 #endif
 
+#define SLIP_RADIO_CONF_NO_PUTCHAR 1
+
 #if defined (UIP_FALLBACK_INTERFACE) || defined (CMD_CONF_OUTPUT)
 #define SLIP_ARCH_CONF_ENABLE      1
 #endif