diff --git a/src/dereko2vec.c b/src/dereko2vec.c
index d7a783a..7c8bb5f 100644
--- a/src/dereko2vec.c
+++ b/src/dereko2vec.c
@@ -1799,7 +1799,8 @@
 void TrainModel() {
 	long a, b, c, d;
 	FILE *fo;
-	pthread_t *pt = (pthread_t *) malloc(num_threads * sizeof(pthread_t));
+	/* one more than num_threads: the monitor thread gets pt[num_threads] */
+	pthread_t *pt = (pthread_t *) malloc((num_threads + 1) * sizeof(pthread_t));
 	threadPos = malloc(num_threads * sizeof(long long));
 	threadIters = malloc(num_threads * sizeof(int));
 	char *timebuf = malloc(80);