diff --git a/actions/subscribe.php b/actions/subscribe.php
index 4c46806e40..a90d7facdf 100644
--- a/actions/subscribe.php
+++ b/actions/subscribe.php
@@ -58,7 +58,7 @@ class SubscribeAction extends Action
 
         $result = subs_subscribe_to($user, $other);
 
-        if($result != true) {
+        if (is_string($result)) {
             $this->clientError($result);
             return;
         }
diff --git a/actions/unsubscribe.php b/actions/unsubscribe.php
index dbb4e41538..6bb10d448b 100644
--- a/actions/unsubscribe.php
+++ b/actions/unsubscribe.php
@@ -87,7 +87,7 @@ class UnsubscribeAction extends Action
 
         $result = subs_unsubscribe_to($user, $other);
 
-        if ($result != true) {
+        if (is_string($result)) {
             $this->clientError($result);
             return;
         }