diff --git a/broker/src/main/java/io/moquette/broker/subscriptions/CTrieSubscriptionDirectory.java b/broker/src/main/java/io/moquette/broker/subscriptions/CTrieSubscriptionDirectory.java
index 8623c45cc..adf322291 100644
--- a/broker/src/main/java/io/moquette/broker/subscriptions/CTrieSubscriptionDirectory.java
+++ b/broker/src/main/java/io/moquette/broker/subscriptions/CTrieSubscriptionDirectory.java
@@ -102,19 +102,27 @@ private static List<Subscription> selectSubscriptionsWithHigherQoSForEachSession
 
     @Override
     public boolean add(Subscription sub) {
-        if (sub.hasShareName()) {
-            throw new IllegalArgumentException("Adding a shared subscription using the non-shared method.");
-        }
+        checkIsShared(sub, "Adding a shared subscription using the non-shared method.");
         boolean notExistingSubscription = ctrie.addToTree(sub);
         subscriptionsRepository.addNewSubscription(sub);
         return notExistingSubscription;
     }
 
-    @Override
-    public void addShared(Subscription sub) {
+    private static void checkIsShared(Subscription sub, String errorMessage) {
+        if (sub.hasShareName()) {
+            throw new IllegalArgumentException(errorMessage);
+        }
+    }
+
+    private static void checkIsNotShared(Subscription sub, String errorMessage) {
         if (!sub.hasShareName()) {
-            throw new IllegalArgumentException("Adding a non-shared subscription using the shared method.");
+            throw new IllegalArgumentException(errorMessage);
         }
+    }
+
+    @Override
+    public void addShared(Subscription sub) {
+        checkIsNotShared(sub, "Adding a non-shared subscription using the shared method.");
         ctrie.addToTree(sub);
         subscriptionsRepository.addNewSharedSubscription(sub);
         List<Subscription> sharedSubscriptions = clientSharedSubscriptions.computeIfAbsent(sub.getClientId(), unused -> new ArrayList<>());
@@ -129,18 +137,14 @@ public void addShared(Subscription sub) {
      */
     @Override
     public void removeSubscription(Subscription sub) {
-        if (sub.hasShareName()) {
-            throw new IllegalArgumentException("Removing a shared subscription using the non-shared method.");
-        }
+        checkIsShared(sub, "Removing a shared subscription using the non-shared method.");
         ctrie.removeFromTree(sub);
         subscriptionsRepository.removeSubscription(sub);
     }
 
     @Override
     public void removeSharedSubscription(Subscription subscription) {
-        if (!subscription.hasShareName()) {
-            throw new IllegalArgumentException("Removing a non-shared subscription using the shared method.");
-        }
+        checkIsNotShared(subscription, "Removing a non-shared subscription using the shared method.");
         ctrie.removeFromTree(subscription);
 
         subscriptionsRepository.removeSharedSubscription(subscription);