diff --git a/index.js b/index.js
index ef84e20..252e35f 100644
--- a/index.js
+++ b/index.js
@@ -586,12 +586,17 @@ class WebUntis {
         });
 
         if (typeof response.data.data !== 'object') throw new Error('Server returned invalid data.');
-        if (
-            !response.data.data.result ||
-            !response.data.data.result.data ||
-            !response.data.data.result.data.elementPeriods ||
-            !response.data.data.result.data.elementPeriods[id]
-        )
+
+        if (response.data.data.error) {
+            /* known codes:
+            * - ERR_TTVIEW_NOTALLOWED_ONDATE
+            */
+            const err = new Error("Server responded with error");
+            err.code = response.data.data.error?.data?.messageKey;
+            throw err;
+        }
+
+        if (!response.data.data.result?.data?.elementPeriods?.[id])
             throw new Error('Invalid response');
 
         const data = response.data.data.result.data;