diff --git a/sys/posix/pthread/pthread.c b/sys/posix/pthread/pthread.c
index bffc6c1ae4..2d48c9fcc0 100644
--- a/sys/posix/pthread/pthread.c
+++ b/sys/posix/pthread/pthread.c
@@ -79,6 +79,7 @@ static char pthread_reaper_stack[PTHREAD_REAPER_STACKSIZE];
 static void pthread_start_routine(void)
 {
     pthread_t self = pthread_self();
+
     pthread_thread_t *pt = pthread_sched_threads[self-1];
     void *retval = pt->start_routine(pt->arg);
     pthread_exit(retval);
@@ -164,7 +165,15 @@ int pthread_create(pthread_t *newthread, const pthread_attr_t *attr, void *(*sta
 
 void pthread_exit(void *retval)
 {
-    pthread_thread_t *self = pthread_sched_threads[pthread_self()-1];
+    pthread_t self_id = pthread_self();
+
+    if (self_id == 0) {
+        DEBUG("ERROR called pthread_self() returned 0 in \"%s\"!\n", __func__);
+        sched_task_exit();
+        return;
+    }
+
+    pthread_thread_t *self = pthread_sched_threads[self_id-1];
 
     while (self->cleanup_top) {
         __pthread_cleanup_datum_t *ct = self->cleanup_top;
@@ -196,6 +205,11 @@ void pthread_exit(void *retval)
 
 int pthread_join(pthread_t th, void **thread_return)
 {
+    if (th < 1 || th > MAXTHREADS) {
+        DEBUG("passed pthread_t th (%d) exceeds bounds of pthread_sched_threads[] in \"%s\"!\n", th, __func__);
+        return -3;
+    }
+
     pthread_thread_t *other = pthread_sched_threads[th-1];
     if (!other) {
         return -1;
@@ -225,6 +239,11 @@ int pthread_join(pthread_t th, void **thread_return)
 
 int pthread_detach(pthread_t th)
 {
+    if (th < 1 || th > MAXTHREADS) {
+        DEBUG("passed pthread_t th (%d) exceeds bounds of pthread_sched_threads[] in \"%s\"!\n", th, __func__);
+        return -2;
+    }
+
     pthread_thread_t *other = pthread_sched_threads[th-1];
     if (!other) {
         return -1;
@@ -286,6 +305,12 @@ int pthread_setcanceltype(int type, int *oldtype)
 void pthread_testcancel(void)
 {
     pthread_t self = pthread_self();
+
+    if (self == 0) {
+        DEBUG("ERROR called pthread_self() returned 0 in \"%s\"!\n", __func__);
+        return;
+    }
+
     if (pthread_sched_threads[self-1]->should_cancel) {
         pthread_exit(PTHREAD_CANCELED);
     }
@@ -293,14 +318,28 @@ void pthread_testcancel(void)
 
 void __pthread_cleanup_push(__pthread_cleanup_datum_t *datum)
 {
-    pthread_thread_t *self = pthread_sched_threads[pthread_self()-1];
+    pthread_t self_id = pthread_self();
+
+    if (self_id == 0) {
+        DEBUG("ERROR called pthread_self() returned 0 in \"%s\"!\n", __func__);
+        return;
+    }
+
+    pthread_thread_t *self = pthread_sched_threads[self_id-1];
     datum->__next = self->cleanup_top;
     self->cleanup_top = datum;
 }
 
 void __pthread_cleanup_pop(__pthread_cleanup_datum_t *datum, int execute)
 {
-    pthread_thread_t *self = pthread_sched_threads[pthread_self()-1];
+    pthread_t self_id = pthread_self();
+
+    if (self_id == 0) {
+        DEBUG("ERROR called pthread_self() returned 0 in \"%s\"!\n", __func__);
+        return;
+    }
+
+    pthread_thread_t *self = pthread_sched_threads[self_id-1];
     self->cleanup_top = datum->__next;
 
     if (execute != 0) {