diff --git a/Connectors.Common/Modules/slt/sltSync.vb b/Connectors.Common/Modules/slt/sltSync.vb
index c0021a6..35d8113 100644
--- a/Connectors.Common/Modules/slt/sltSync.vb
+++ b/Connectors.Common/Modules/slt/sltSync.vb
@@ -55,6 +55,11 @@ Namespace slt
                         Logger.Info("ExtDocId: [{0}]", oDocument.ExtDocId)
 
                         Dim oFileName = oDocument.GetUniqueFilename()
+
+                        If oFileName Is Nothing Then
+                            Throw New ApplicationException("Filename or extension could not be determined!")
+                        End If
+
                         Dim oFilePath = GetFinalFilePath(oFileName)
 
                         If CopyFileToOutputPath(oDocument.Data, oFilePath) = False Then