diff --git a/runners/flink/flink_runner.gradle b/runners/flink/flink_runner.gradle
index e40c05aa732a..79244525320a 100644
--- a/runners/flink/flink_runner.gradle
+++ b/runners/flink/flink_runner.gradle
@@ -249,7 +249,7 @@ def createValidatesRunnerTask(Map m) {
     def pipelineOptionsArray = ["--runner=TestFlinkRunner",
                                 "--streaming=${config.streaming}",
                                 "--useDataStreamForBatch=${config.useDataStreamForBatch}",
-                                "--parallelism=2",
+                                "--parallelism=1",
     ]
     if (config.checkpointing) {
       pipelineOptionsArray.addAll([