diff --git a/include/villas/shmem.h b/include/villas/shmem.h
index 5811eb2b0..93da15a72 100644
--- a/include/villas/shmem.h
+++ b/include/villas/shmem.h
@@ -19,6 +19,8 @@ struct shmem_shared {
 	union shmem_queue out; /**< Queue for samples passed from node to external program.*/
 	int cond_out; /**< Whether to use a pthread_cond_t to signal if new samples are written to outqueue. */
 	struct pool pool; /**< Pool for the samples in the queues. */
+	pthread_barrier_t start_bar;
+	pthread_barrierattr_t start_attr;
 	atomic_size_t node_stopped;
 	atomic_size_t ext_stopped;
 };
diff --git a/lib/nodes/shmem.c b/lib/nodes/shmem.c
index e2f5435c3..9246608cf 100644
--- a/lib/nodes/shmem.c
+++ b/lib/nodes/shmem.c
@@ -89,8 +89,14 @@ int shmem_open(struct node *n) {
 	if (pool_init(&shm->shared->pool, shm->insize+shm->outsize, SAMPLE_LEN(shm->sample_size), shm->manager) < 0)
 		error("Shm pool allocation failed (not enough memory?)");
 
+	pthread_barrierattr_init(&shm->shared->start_attr);
+	pthread_barrierattr_setpshared(&shm->shared->start_attr, PTHREAD_PROCESS_SHARED);
+	pthread_barrier_init(&shm->shared->start_bar, &shm->shared->start_attr, 2);
+
 	if (shm->exec && !spawn(shm->exec[0], shm->exec))
 		serror("Failed to spawn external program");
+
+	pthread_barrier_wait(&shm->shared->start_bar);
 	return 0;
 }
 
diff --git a/lib/shmem.c b/lib/shmem.c
index 7feab1ff9..70c491f0c 100644
--- a/lib/shmem.c
+++ b/lib/shmem.c
@@ -49,7 +49,9 @@ struct shmem_shared* shmem_shared_open(const char *name, void **base_ptr)
 	cptr = (char *) base + sizeof(struct memtype) + sizeof(struct memblock);
 	if (base_ptr)
 		*base_ptr = base;
-	return (struct shmem_shared *) cptr;
+	shm = (struct shmem_shared *) cptr;
+	pthread_barrier_wait(&shm->start_bar);
+	return shm;
 }
 
 int shmem_shared_close(struct shmem_shared *shm, void *base)