diff --git a/amazon-kinesis-client-multilang/src/main/java/software/amazon/kinesis/multilang/NestedPropertyKey.java b/amazon-kinesis-client-multilang/src/main/java/software/amazon/kinesis/multilang/NestedPropertyKey.java
index 9902d28c..13acfeb1 100644
--- a/amazon-kinesis-client-multilang/src/main/java/software/amazon/kinesis/multilang/NestedPropertyKey.java
+++ b/amazon-kinesis-client-multilang/src/main/java/software/amazon/kinesis/multilang/NestedPropertyKey.java
@@ -15,6 +15,7 @@
 package software.amazon.kinesis.multilang;
 
 import java.util.HashMap;
+import java.util.List;
 import java.util.Map;
 
 import com.google.common.base.CaseFormat;
@@ -73,8 +74,13 @@ public enum NestedPropertyKey {
      * @see <a href="https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/using-regions-availability-zones.html#concepts-regions">Available Regions</a>
      */
     ENDPOINT_REGION {
-        void visit(final NestedPropertyProcessor processor, final String region) {
-            processor.acceptEndpointRegion(Region.of(region));
+        void visit(final NestedPropertyProcessor processor, final String regionName) {
+            List<Region> validRegions = Region.regions();
+            Region region = Region.of(regionName);
+            if (!validRegions.contains(region)) {
+                throw new IllegalArgumentException("Invalid region name: " + regionName);
+            }
+            processor.acceptEndpointRegion(region);
         }
     },
 
diff --git a/amazon-kinesis-client-multilang/src/test/java/software/amazon/kinesis/multilang/NestedPropertyKeyTest.java b/amazon-kinesis-client-multilang/src/test/java/software/amazon/kinesis/multilang/NestedPropertyKeyTest.java
index 350b9fac..3c2de9c9 100644
--- a/amazon-kinesis-client-multilang/src/test/java/software/amazon/kinesis/multilang/NestedPropertyKeyTest.java
+++ b/amazon-kinesis-client-multilang/src/test/java/software/amazon/kinesis/multilang/NestedPropertyKeyTest.java
@@ -70,10 +70,7 @@ public class NestedPropertyKeyTest {
         verify(mockProcessor).acceptEndpointRegion(expectedRegion);
     }
 
-    //    Region.of(), which is invoked in this test, no longer throws an IllegalArgumentException when given an invalid
-    // region
-    //    We would need to implement our own region validation to maintain this test
-    //    @Test(expected = IllegalArgumentException.class)
+    @Test(expected = IllegalArgumentException.class)
     public void testInvalidEndpointRegion() {
         parse(mockProcessor, createKey(ENDPOINT_REGION, "snuffleupagus"));
     }