diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9890a9d..a0d0533 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,9 @@
 
 All Notable changes to `activitylog` will be documented in this file
 
+### 2.1.1
+- Only use configured default user id if it is numeric
+
 ### 2.1.0
 - Added option to specify a default user id
 
diff --git a/src/Spatie/Activitylog/ActivitylogSupervisor.php b/src/Spatie/Activitylog/ActivitylogSupervisor.php
index 91a1ed4..2fc3e28 100644
--- a/src/Spatie/Activitylog/ActivitylogSupervisor.php
+++ b/src/Spatie/Activitylog/ActivitylogSupervisor.php
@@ -96,6 +96,10 @@ public function normalizeUserId($userId)
             return $this->auth->user()->id;
         }
 
-        return $this->config->get('activitylog.defaultUserId');
+        if (is_numeric($this->config->get('activitylog.defaultUserId'))) {
+            return $this->config->get('activitylog.defaultUserId');
+        };
+
+        return '';
     }
 }