diff --git a/src/main/java/io/github/robwin/swagger/test/ConsumerDrivenValidator.java b/src/main/java/io/github/robwin/swagger/test/ConsumerDrivenValidator.java
index d6321b5..4c21682 100644
--- a/src/main/java/io/github/robwin/swagger/test/ConsumerDrivenValidator.java
+++ b/src/main/java/io/github/robwin/swagger/test/ConsumerDrivenValidator.java
@@ -155,7 +155,7 @@ private void validateDefinition(String definitionName, Model actualDefinition, M
                                          schemaObjectResolver.resolvePropertiesFromExpected(expectedDefinition),
                                          definitionName);
 
-            if (expectedDefinition instanceof ModelImpl) {
+            if (expectedDefinition instanceof ModelImpl && actualDefinition instanceof ModelImpl) {
                 validateDefinitionRequiredProperties(((ModelImpl) actualDefinition).getRequired(),
                                                      ((ModelImpl) expectedDefinition).getRequired(),
                                                        definitionName);
diff --git a/src/main/java/io/github/robwin/swagger/test/DocumentationDrivenValidator.java b/src/main/java/io/github/robwin/swagger/test/DocumentationDrivenValidator.java
index 71377e9..f1aecaa 100644
--- a/src/main/java/io/github/robwin/swagger/test/DocumentationDrivenValidator.java
+++ b/src/main/java/io/github/robwin/swagger/test/DocumentationDrivenValidator.java
@@ -154,7 +154,7 @@ private void validateDefinition(String definitionName, Model actualDefinition, M
                                          schemaObjectResolver.resolvePropertiesFromExpected(expectedDefinition),
                                          definitionName);
 
-            if (expectedDefinition instanceof ModelImpl) {
+            if (expectedDefinition instanceof ModelImpl && actualDefinition instanceof ModelImpl) {
                 validateDefinitionRequiredProperties(((ModelImpl) actualDefinition).getRequired(),
                                                      ((ModelImpl) expectedDefinition).getRequired(),
                                                        definitionName);