diff --git a/ocpp-v1_6/src/main/java/eu/chargetime/ocpp/model/firmware/DiagnosticsStatusNotificationConfirmation.java b/ocpp-v1_6/src/main/java/eu/chargetime/ocpp/model/firmware/DiagnosticsStatusNotificationConfirmation.java
index a0521234f..d94ad75b2 100644
--- a/ocpp-v1_6/src/main/java/eu/chargetime/ocpp/model/firmware/DiagnosticsStatusNotificationConfirmation.java
+++ b/ocpp-v1_6/src/main/java/eu/chargetime/ocpp/model/firmware/DiagnosticsStatusNotificationConfirmation.java
@@ -30,6 +30,7 @@
 import eu.chargetime.ocpp.model.Confirmation;
 
 import javax.xml.bind.annotation.XmlRootElement;
+import java.util.Objects;
 
 /**
  * Sent by the Charge Point to the Central System in response to an {@link DiagnosticsStatusNotificationRequest}.
@@ -52,7 +53,7 @@ public boolean equals(Object o) {
 
     @Override
     public int hashCode() {
-        return 5;
+        return Objects.hash(DiagnosticsStatusNotificationConfirmation.class);
     }
 
     @Override
diff --git a/ocpp-v1_6/src/main/java/eu/chargetime/ocpp/model/firmware/FirmwareStatusNotificationConfirmation.java b/ocpp-v1_6/src/main/java/eu/chargetime/ocpp/model/firmware/FirmwareStatusNotificationConfirmation.java
index 371990c46..168f07968 100644
--- a/ocpp-v1_6/src/main/java/eu/chargetime/ocpp/model/firmware/FirmwareStatusNotificationConfirmation.java
+++ b/ocpp-v1_6/src/main/java/eu/chargetime/ocpp/model/firmware/FirmwareStatusNotificationConfirmation.java
@@ -31,6 +31,7 @@
 
 import javax.xml.bind.annotation.XmlElement;
 import javax.xml.bind.annotation.XmlRootElement;
+import java.util.Objects;
 
 /**
  * Sent by the Charge Point to the Central System in response to an {@link FirmwareStatusNotificationRequest}.
@@ -53,7 +54,7 @@ public boolean equals(Object o) {
 
     @Override
     public int hashCode() {
-        return 6;
+        return Objects.hash(FirmwareStatusNotificationConfirmation.class);
     }
 
     @Override
diff --git a/ocpp-v1_6/src/main/java/eu/chargetime/ocpp/model/firmware/UpdateFirmwareConfirmation.java b/ocpp-v1_6/src/main/java/eu/chargetime/ocpp/model/firmware/UpdateFirmwareConfirmation.java
index 3a45daa5e..edda07dcf 100644
--- a/ocpp-v1_6/src/main/java/eu/chargetime/ocpp/model/firmware/UpdateFirmwareConfirmation.java
+++ b/ocpp-v1_6/src/main/java/eu/chargetime/ocpp/model/firmware/UpdateFirmwareConfirmation.java
@@ -31,6 +31,7 @@
 
 import javax.xml.bind.annotation.XmlElement;
 import javax.xml.bind.annotation.XmlRootElement;
+import java.util.Objects;
 
 /**
  * Sent by the Charge Point to the Central System in response to an {@link UpdateFirmwareRequest}.
@@ -53,7 +54,7 @@ public boolean equals(Object o) {
 
     @Override
     public int hashCode() {
-        return 7;
+        return Objects.hash(UpdateFirmwareConfirmation.class);
     }
 
     @Override
diff --git a/ocpp-v1_6/src/main/java/eu/chargetime/ocpp/model/firmware/UpdateFirmwareRequest.java b/ocpp-v1_6/src/main/java/eu/chargetime/ocpp/model/firmware/UpdateFirmwareRequest.java
index 384419671..2d06ecb80 100644
--- a/ocpp-v1_6/src/main/java/eu/chargetime/ocpp/model/firmware/UpdateFirmwareRequest.java
+++ b/ocpp-v1_6/src/main/java/eu/chargetime/ocpp/model/firmware/UpdateFirmwareRequest.java
@@ -46,7 +46,7 @@ public class UpdateFirmwareRequest implements Request {
     private String location;
     private Integer retries;
     private Calendar retrieveDate;
-    private int retryInterval;
+    private Integer retryInterval;
 
     public UpdateFirmwareRequest() {}
 
@@ -131,7 +131,7 @@ public void setRetrieveDate(Calendar retrieveDate) {
      *
      * @return int, retry interval.
      */
-    public int getRetryInterval() {
+    public Integer getRetryInterval() {
         return retryInterval;
     }
 
@@ -145,7 +145,7 @@ public int getRetryInterval() {
      * 
      */
     @XmlElement
-    public void setRetryInterval(int retryInterval) throws PropertyConstraintException {
+    public void setRetryInterval(Integer retryInterval) throws PropertyConstraintException {
         if (retryInterval <= 0)
             throw new PropertyConstraintException("retryInterval", retryInterval);
 
@@ -162,7 +162,7 @@ public boolean equals(Object o) {
         if (this == o) return true;
         if (o == null || getClass() != o.getClass()) return false;
         UpdateFirmwareRequest that = (UpdateFirmwareRequest) o;
-        return retryInterval == that.retryInterval &&
+        return retryInterval.equals(that.retryInterval) &&
             Objects.equals(location, that.location) &&
             Objects.equals(retries, that.retries) &&
             Objects.equals(retrieveDate, that.retrieveDate);