diff --git a/process/Importer_lib/process.js b/process/Importer_lib/process.js
index a9e5a528933faecd47bc7480712b8a2114e3787b..98cb4591bf894ae46a7b4a1796cbe5b66b08e525 100644
--- a/process/Importer_lib/process.js
+++ b/process/Importer_lib/process.js
@@ -1443,6 +1443,10 @@ function Importer(pConfig)
             var tmp = this.KeyColumn[pTable][col];  // contains I | I;U | I+U
             if(tmp != "")
             {
+                if(!this.OutputRecord[pTable][col])
+                {
+                    throw new Error(translate.withArguments("Importer_lib: Condition could not be build because the Keycolumn %0 is not in the OutputRecord.", [col]));
+                }
                 var value = this.OutputRecord[pTable][col]["U"];
                 if(value == undefined || value == "")
                     value = this.OutputRecord[pTable][col]["I+U"];