diff --git a/tests/run-multitests.py b/tests/run-multitests.py
index 3163a48e63..66ca799675 100755
--- a/tests/run-multitests.py
+++ b/tests/run-multitests.py
@@ -243,6 +243,7 @@ def trace_instance_output(instance_idx, line):
     if cmd_args.trace_output:
         t_ms = round((time.time() - trace_t0) * 1000)
         print("{:6} i{} :".format(t_ms, instance_idx), line)
+        sys.stdout.flush()
 
 
 def run_test_on_instances(test_file, num_instances, instances):