diff --git a/modules/core/lib/Auth/Process/AttributeAlter.php b/modules/core/lib/Auth/Process/AttributeAlter.php
index 0008fc3658c8c7f386ee4db47976b8c41bd492f4..d8e9e6a0f4716d9e2262f6b8a27bc18fc36a265e 100644
--- a/modules/core/lib/Auth/Process/AttributeAlter.php
+++ b/modules/core/lib/Auth/Process/AttributeAlter.php
@@ -152,7 +152,7 @@ class sspmod_core_Auth_Process_AttributeAlter extends SimpleSAML_Auth_Processing
                     if ($this->subject === $this->target) {
                         $value = $new_value;
                     } else {
-                        $attributes[$this->target][] = $new_value;
+                        $attributes[$this->target] = array($new_value);
                     }
                 }
             }