diff --git a/Code/BasicFilters/otbMaskMuParserFilter.txx b/Code/BasicFilters/otbMaskMuParserFilter.txx
index 92d07ce717f9bfe05a46c9121a796904dc29db20..2a791411a29310dabe27832576b30c09b3c139b6 100644
--- a/Code/BasicFilters/otbMaskMuParserFilter.txx
+++ b/Code/BasicFilters/otbMaskMuParserFilter.txx
@@ -38,7 +38,7 @@ MaskMuParserFilter<TInputImage, TOutputImage, TFunction>::MaskMuParserFilter()
   m_OverflowCount = 0;
   m_ThreadUnderflow.SetSize(1);
   m_ThreadOverflow.SetSize(1);
-
+  m_Expression="";
 }
 
 // Destructor