diff --git a/teckidscal.sty b/teckidscal.sty
index a703c34a8f4bd6d15b3048ec041042f5b5b133af..f1f785dbbd63e5544d939f53cfe2b35b9712e139 100644
--- a/teckidscal.sty
+++ b/teckidscal.sty
@@ -284,8 +284,13 @@
  \fi%
 }%
 
-\newcommand{\teckidscalonline}[1]{%
- \tkToJD{#1}%
+\newcommand{\teckidscalonline}[2][teckidsargdefaulted]{%
+ \tkToJD{#2}%
+ \ifstrequal{#1}{teckidsargdefaulted}{}{%
+  \tkifdef{tkDayTeckids\number\tkjd}{\PackageError{teckidscal}%
+   {Ein Tag kann nur ein Label haben! Fehler in Tag #2}{}}{}%
+  \expandafter\xdef\csname tkDayTeckids\number\tkjd\endcsname{#1}%
+ }%
  \tk@BoldenDay%
  \ifcase\csname tkDayType\number\tkjd\endcsname\or\else%
   \PackageError{teckidscal}%