diff --git a/microsim/interface.cpp b/microsim/interface.cpp

index da035e9..737da09 100755

--- a/microsim/interface.cpp

+++ b/microsim/interface.cpp

@@ -317,7 +317,7 @@ extern int open_cod_file(Processor **, char *);

 int Interface::open(const char *file)

 {

-    char *str;

+    const char *str;

     str = strrchr(file,'.');

     if(str==NULL)