diff --git a/core/sys/rtimer.c b/core/sys/rtimer.c
index bf59498b2..af8b2a037 100644
--- a/core/sys/rtimer.c
+++ b/core/sys/rtimer.c
@@ -28,13 +28,13 @@
  *
  * This file is part of the Contiki operating system.
  *
- * @(#)$Id: rtimer.c,v 1.2 2007/03/28 20:28:22 adamdunkels Exp $
+ * @(#)$Id: rtimer.c,v 1.3 2007/05/17 00:23:58 adamdunkels Exp $
  */
 
 #include "sys/rtimer.h"
 #include "contiki.h"
 
-#define LIST_SIZE 16
+#define LIST_SIZE 4
 
 static struct rtimer *rtimers[LIST_SIZE];
 static u8_t next, firstempty;
@@ -78,6 +78,12 @@ rtimer_set(struct rtimer *rtimer, rtimer_clock_t time, rtimer_clock_t duration,
   for(i = next; i != firstempty;
       i = (i + 1) % LIST_SIZE) {
 
+    if(rtimers[i] == rtimer) {
+      /* Check if timer is already scheduled. If so, we do not
+	 schedule it again. */
+      return RTIMER_ERR_ALREADY_SCHEDULED;
+      
+    }
     /* XXX: should check a range of time not just the same precise
        moment. */
     if(rtimers[i]->time == time) {
@@ -89,7 +95,7 @@ rtimer_set(struct rtimer *rtimer, rtimer_clock_t time, rtimer_clock_t duration,
   /* Put the rtimer at the end of the rtimer list. */
   rtimer->time = time;
   rtimers[firstempty] = rtimer;
-  PRINTF("rtimer_post: putting rtimer %s as %d\n", rtimer->name, firstempty);
+  PRINTF("rtimer_post: putting rtimer %p as %d\n", rtimer, firstempty);
 
   firstempty = (firstempty + 1) % LIST_SIZE;
 
@@ -100,8 +106,8 @@ rtimer_set(struct rtimer *rtimer, rtimer_clock_t time, rtimer_clock_t duration,
      run the rtimer_arch_schedule() function to get the ball rolling. */
   if(firstempty == (next + 1) % LIST_SIZE) {
     
-    PRINTF("rtimer_set scheduling %d %s (%d)\n",
-	 next, rtimers[next]->name, rtimers[next]->time);
+    PRINTF("rtimer_set scheduling %d %p (%d)\n",
+	 next, rtimers[next], rtimers[next]->time);
     rtimer_arch_schedule(rtimers[next]->time);
   }
   
@@ -114,13 +120,18 @@ rtimer_run_next(void)
   int i, n;
   struct rtimer *t;
 
+  /* Do not run timer if list is empty. */
+  if(next == firstempty) {
+    return;
+  }
+  
   t = rtimers[next];
 
   /* Increase the pointer to the next rtimer. */
   next = (next + 1) % LIST_SIZE;
   
   /* Run the rtimer. */
-  PRINTF("rtimer_run_next running %s\n", t->name);
+  PRINTF("rtimer_run_next running %p\n", t);
   t->func(t, t->ptr);
 
   if(next == firstempty) {
@@ -132,24 +143,24 @@ rtimer_run_next(void)
   /* Find the next rtimer to run. */
   n = next;
   for(i = next; i != firstempty; i = (i + 1) % LIST_SIZE) {
-    PRINTF("rtimer_run_next checking %s (%d) against %s (%d)\n",
-	   rtimers[i]->name, rtimers[i]->time,
-	   rtimers[n]->name, rtimers[n]->time);
+    PRINTF("rtimer_run_next checking %p (%d) against %p (%d)\n",
+	   rtimers[i], rtimers[i]->time,
+	   rtimers[n], rtimers[n]->time);
     if(RTIMER_CLOCK_LT(rtimers[i]->time, rtimers[n]->time)) {
       n = i;
     }
   }
 
-  PRINTF("rtimer_run_next next rtimer is %d %s (%d)\n",
-	 n, rtimers[n]->name, rtimers[n]->time);
+  PRINTF("rtimer_run_next next rtimer is %d %p (%d)\n",
+	 n, rtimers[n], rtimers[n]->time);
   
   /* Put the next rtimer first in the rtimer list. */
   t = rtimers[next];
   rtimers[next] = rtimers[n];
   rtimers[n] = t;
 
-  PRINTF("rtimer_run_next scheduling %d %s (%d)\n",
-	 next, rtimers[next]->name, rtimers[next]->time);
+  PRINTF("rtimer_run_next scheduling %d %p (%d)\n",
+	 next, rtimers[next], rtimers[next]->time);
 
   rtimer_arch_schedule(rtimers[next]->time);
 }