diff --git a/modules/io/src/mol/star_parser.hh b/modules/io/src/mol/star_parser.hh
index 6e62f6bfa1fdeb25a39c25f32dfc893b5143a51a..cde608ccbae7a412919831bc860ad54723ba0ffe 100644
--- a/modules/io/src/mol/star_parser.hh
+++ b/modules/io/src/mol/star_parser.hh
@@ -158,7 +158,7 @@ public:
   }
 
   /// \brief retrieve the line, the parser is currently working on
-  int GetCurrentLinenum()
+  int GetCurrentLinenum() const
   {
     return line_num_;
   }