diff --git a/lib/src/main/java/com/diffplug/spotless/markdown/FlexmarkStep.java b/lib/src/main/java/com/diffplug/spotless/markdown/FlexmarkStep.java
index 5e0193bf39..ad3f883996 100644
--- a/lib/src/main/java/com/diffplug/spotless/markdown/FlexmarkStep.java
+++ b/lib/src/main/java/com/diffplug/spotless/markdown/FlexmarkStep.java
@@ -39,7 +39,7 @@ public class FlexmarkStep implements Serializable {
 	public static final String NAME = "flexmark-java";
 
 	private final Promised jarState;
-	private final MutableDataSet options;
+	private final transient MutableDataSet options;
 
 	private FlexmarkStep(
 		final Promised jarState,