diff --git a/test/command/test_fluentd.rb b/test/command/test_fluentd.rb
index 2ca08f5779..042c2c70db 100644
--- a/test/command/test_fluentd.rb
+++ b/test/command/test_fluentd.rb
@@ -230,10 +230,10 @@ def assert_fluentd_fails_to_start(cmdline, *pattern_list, timeout: 20)
       execute_command(cmdline) do |pid, stdout|
         begin
           waiting(timeout) do
-            while process_exist?(pid) && !running
+            until running
               readables, _, _ = IO.select([stdout], nil, nil, 1)
               next unless readables
-              next if readables.first.eof?
+              break if readables.first.eof?
 
               stdio_buf << eager_read(readables.first)
               lines = stdio_buf.split("\n")