diff --git a/core/src/test/java/com/opensymphony/xwork2/validator/DateRangeValidatorTest.java b/core/src/test/java/com/opensymphony/xwork2/validator/DateRangeValidatorTest.java
index a8f64e958..98a5ed051 100644
--- a/core/src/test/java/com/opensymphony/xwork2/validator/DateRangeValidatorTest.java
+++ b/core/src/test/java/com/opensymphony/xwork2/validator/DateRangeValidatorTest.java
@@ -48,6 +48,7 @@ public class DateRangeValidatorTest extends XWorkTestCase {
         HashMap<String, Object> params = new HashMap<>();
         params.put("date", date.getTime());
         context.put(ActionContext.PARAMETERS, HttpParameters.create(params).build());
+        context.put(ActionContext.LOCALE, Locale.US);  // Force US Locale for date conversion tests on JDK9+
 
         ActionProxy proxy = actionProxyFactory.createActionProxy("", MockConfigurationProvider.VALIDATION_ACTION_NAME, null, context);
         proxy.execute();
diff --git a/core/src/test/java/com/opensymphony/xwork2/validator/VisitorFieldValidatorTest.java b/core/src/test/java/com/opensymphony/xwork2/validator/VisitorFieldValidatorTest.java
index cd66aca2f..c1f090444 100644
--- a/core/src/test/java/com/opensymphony/xwork2/validator/VisitorFieldValidatorTest.java
+++ b/core/src/test/java/com/opensymphony/xwork2/validator/VisitorFieldValidatorTest.java
@@ -38,6 +38,7 @@ public class VisitorFieldValidatorTest extends XWorkTestCase {
     public void setUp() throws Exception {
         super.setUp();
 
+        ActionContext.getContext().put(ActionContext.LOCALE, Locale.US);  // Force US Locale for date conversion tests on JDK9+
         action = container.inject(VisitorValidatorTestAction.class);
 
         TestBean bean = action.getBean();