diff --git a/testing/getprime/getprime_main.c b/testing/getprime/getprime_main.c
index 198f4a5ca..910aef797 100644
--- a/testing/getprime/getprime_main.c
+++ b/testing/getprime/getprime_main.c
@@ -102,8 +102,7 @@ static FAR void *thread_func(FAR void *param)
   printf("thread #%d finished, found %d primes, last one was %d\n",
          no, count, last);
 
-  pthread_exit(NULL);
-  return NULL; /* To keep some compilers happy */
+  return NULL;
 }
 
 /****************************************************************************
@@ -141,6 +140,14 @@ static void get_prime_in_parallel(int n)
   printf("Set thread policy to SCHED_FIFO\n");
 #endif
 
+  /* Zero threads, do work from main thread instead. */
+
+  if (n == 0)
+    {
+        arg[0] = n;
+        thread_func((FAR void *)&arg[0]);
+    }
+
   for (i = 0; i < n; i++)
     {
       arg[i] = i;
@@ -161,6 +168,19 @@ static void get_prime_in_parallel(int n)
   UNUSED(status);
 }
 
+/****************************************************************************
+ * Name: usage
+ ****************************************************************************/
+
+static void usage(void)
+{
+    printf("\nUsage: getprime [<num_threads>]\n");
+    printf("\nWhere:\n");
+    printf("  <num_threads> is integer from 0 to %d (default 1).\n",
+           MAX_THREADS);
+    exit(0);
+}
+
 /****************************************************************************
  * Public Functions
  ****************************************************************************/
@@ -180,9 +200,14 @@ int main(int argc, FAR char *argv[])
   if (argc == 2)
     {
       n = (int)strtol(argv[1], &endp, 10);
-      ASSERT(argv[1] != endp);
-
-      ASSERT(0 < n && n <= MAX_THREADS);
+      if (argv[1] == endp || n < 0 || n > MAX_THREADS)
+        {
+            usage();
+        }
+    }
+  else if (argc > 2)
+    {
+      usage();
     }
 
   clock_gettime(CLOCK_REALTIME, &ts0);