diff --git a/Monitoring Client/module.php b/Monitoring Client/module.php
index 5dea58d..014bdfd 100644
--- a/Monitoring Client/module.php	
+++ b/Monitoring Client/module.php	
@@ -271,7 +271,9 @@ class MonitoringClient extends IPSModule {
      */
     private function getCategoryVariables($categoryId) {
         $variables = array();
-        if (!IPS_CategoryExists($categoryId)) {
+        // Unconfigured client categories use -1. IPS_CategoryExists() rejects
+        // negative IDs before it can return false.
+        if ($categoryId < 1 || !IPS_CategoryExists($categoryId)) {
             return $variables;
         }
 
diff --git a/library.json b/library.json
index b1bf691..fda9eff 100644
--- a/library.json
+++ b/library.json
@@ -8,6 +8,6 @@
         "date": 1491343200
     },
     "version": "3.0",
-    "build": 1,
+    "build": 2,
     "date": 0
-}
\ No newline at end of file
+}