diff --git a/core/src/main/java/hudson/tasks/BuildTrigger.java b/core/src/main/java/hudson/tasks/BuildTrigger.java
index 99fabf40ef23c3d1353f4397a02cf59b273069ef..ef0fadaa9eff9d67bdd66471d133687079b50bd7 100644
--- a/core/src/main/java/hudson/tasks/BuildTrigger.java
+++ b/core/src/main/java/hudson/tasks/BuildTrigger.java
@@ -185,7 +185,7 @@ public class BuildTrigger extends Publisher {
         public Publisher newInstance(StaplerRequest req, JSONObject formData) throws FormException {
             return new BuildTrigger(
                 formData.getString("childProjects"),
-                formData.getBoolean("evenIfUnstable"));
+                formData.has("evenIfUnstable") && formData.getBoolean("evenIfUnstable"));
         }
 
         @Override